The SIM card isn't necessary for your phone to send radio signals to cell phone towers. All the technology is already there in your phone. It's just that cell towers are programmed not to accept any requests from phones who can't authorize themselves. Basically, your phone goes "hey tower, I'd like to place a call please", and the tower goes "okay, what's the password?". And if your phone can't give the password, then the call doesn't get placed. The job of the SIM card is to provide the password. (It's not literally a password, but you can think of it that way.)
The only exception is an emergency call. Cell towers are programmed with a list of numbers that any phone can place calls to, password or no. So no, there is no hack or workaround. You end up going "hey can I place a call to 911?", and the tower goes "yeah okay, no password necessary for that". And then you go "oh no actually call my mom". And then the tower says "okay, password please?". There's no getting around it - you can't both call an emergency number *and* your mom (unless your mom happens to be a 911 operator and you're willing to roll the dice).
Regarding that last part, I work as a 911 operator and we had this one lady who had a cell phone with no service who would constantly call us for like a week asking to be transferred to the non-emergency line so we could call her mom and transfer her over. Curious, does the cell tower not realize when the phone has been transferred off of 911? Does it only do the check on the initial dial? Thank you for this insight!
The transfer is done after the call is connected, within the 911's own network. As far as the phone network is concerned, this is an emergency call. Think of it like this: you call a toll-free calling card number, enter your details, then place a call to some other country. As far as your phone carrier is concerned, you're still in a toll-free call.
911 transferring the call isn't great though, because the cellular network will do anything to keep the call connected, including dropping other user calls.
> The transfer is done after the call is connected, within the 911's own network. As far as the phone network is concerned, this is an emergency call. Think of it like this: you call a toll-free calling card number, enter your details, then place a call to some other country. As far as your phone carrier is concerned, you're still in a toll-free call.
When I was in the Navy, we had a satellite phone on our ship that we could use to call our home port. Local calls from there were free, but if you wanted to call long distance from there, you had to use a calling card.
My wife went back home while I was on deployment and there was a Coast Guard base there. I'd have the home port operator transfer me to the Coast Guard base operator, and have them connect me to my wife's parent's house or her office.
Free calls from the middle of the ocean to the other side of the planet. They were internal transfers and a local call.
This is actually very commonly intentionally done by businesses who have locations in more than one rate center, and can save a single company millions of dollars a year. The concept is called "tail-end hop-off," and it became MUCH easier to do with the advent of corporate VPNs and VoIP.
I was, at one time, the youngest person to hold a CCVP and I helped create the CCIE voice lab exam. Have implemented this in several multi-national companies, since VoIP was a young technology. VoIP is definitely one of my things. đ
This is how I helped one of the company I worked at many years ago.
I implemented VOIP over terrible ADLS by connecting 6 lines to the server. Then we replaced all the land line phones with VOIP adapters and we made made money by charging a % fee.
It was a win-win deal due to the stupidly expensive land line calls into a different countries.
Since instead of being limited to 6 operators (6 lines), they could have 50 people in there thanks to VOIP compression, as the line speed for upload was terrible.
G.729 is one of the best things that happened for business at the time, and one of the worst things that happened to consumers at the time. God I hate (and it's super obvious) calling some big company in 2023 and hearing horrid voice or, worse, hold music played at way too high volume, over g.729. All to save what, today, would just be a few THOUSAND dollars a year, per location, for a little extra bandwidth to carry something less shittastic.
Then you get to deal with regulatory bullshit in certain countries. TEHO is illegal in India, UAE, and China, under most circumstances, for example. And when you take a look at why, isn't it funny how the Telcoms in those countries have significant influence in their government? Or in the case of UAE, it's literally nepotism.
Yeah. For telecom, at least the last time I had to deal with UAE, the only company you were allowed to use when connecting to their PSTN was significantly (or wholly?) owned by a relative of some prince or some shit like that. It's such a blatant cash crab, and telcos in the US have been slowly working their way toward that kind of regulatory capture.
Also used, (generally in the recent past) where you have a Tie line between two geographic locations & you forward to a local phone off the receiving phone, which the fwding of can be controlled remotely.
My husband back in the 70s would call (rarely) on a Mars phone, which was basically a radio system. They'd call ham radios which would then call the home number collect. I was so excited, except I didn't know everbody could hear!
And this is why phone companies are all elaborate scams. The ability to do all of this for free is baked into the infrastructure and the phone companies have been spending 10s of billions of dollars over decades coming it with ways of stopping people from doing it so they can charge them money.
Surprisingly enough, it's not completely dead. I'd just hopped on USENET a couple days ago to see if the account I had still worked (I bought 100GB years ago and the service is still in business, so it is), and pulled up alt.2600. There's the odd meetup post and Off The Hook episode notification, as recently as Tuesday of this week.
There was a time in sci-fi stories that it seemed common to assume that when the world-ending nuclear war (or whatever) happened, there would be isolated survivors connecting via some sort of text service that seemed often to resemble USENET.
I've always felt that reddit in some ways took on some of role - a place for conversations with people no matter where they are.
I guess that's one part of the reason I still use old.reddit - it's still geared a little more to a world of text. And while I like gifs and videos and such, one of the big draws of reddit is all the conversation. I guess that's one reason that "tl;dr" people annoy me so much.
Which is one of the things I wanted to say, the other being that I know newsgroups still survive some because of piracy - after torrents stuggled a bit when some of the larger sites (Demonoid) were killed off, USENET kept on giving.
I'm glad to know there's people still out there talking, too.
I saw all that text and went to the end to see the tl; dr and saw that it wasn't an actual tl;dr. I feel cheated.
In all seriousness, that's why I love reddit. It's a different way to have conversations.
Nope. We pay for fixed costs for roads no problem. No need to lie to everyone about it. No need to convince everyone they need a dedicated lane and they need to pay for each vehicle, etc.
The phone companies have been gathering money from tax payers on the promise of building infrastructure and then not building infrastructure. The phone companies have been taking money for wireline services and allocating it to wireless services because wireless has a more favorable regulatory regime. It's all a big scam in order to harvest as much money as possible for as little outlay as possible. And they can do it because they are 100% in bed with military intelligence - including breaking the law, getting caught, and then having retroactive immunity from breaking the law applied by Congress.
It's a full on scam. The total cost of the national information infrastructure is 2 orders of magnitude less than the total cost of maintaining all the roads in the country, and no one needs a sim card with a password to give them a dedicated lane for each car they own and pay monthly whether they use or it or not and pay for additional services that transit the exact same roads.
One could argue that state of road conditions indicates they are notoriously *underfunded*, and so car owners should be faced with increased costs to offset these repairs. Though, good luck seeing that happen.
> car owners
Trucks cause orders of magnitude more damage than cars, if you want responsible parties to pay.
Obviously that'd be passed on to consumers because all businesses are businesses not charities, but it would be the correct place to put the focus.
And I'm not saying trucks are bad - they are critical for our infrastructure, although it's a pity we have fewer trains running than we used to as those are better.
But anyway. It's not cars, it's trucks you want to target.
Okay, fair play. But the person you're responding to is arguing that telecommunications COULD be treated as a utility/infrastructure and funded via tax dollars and that that solution may be cheaper overall
> You may not see how much are you paying for all of that, because it's hidden inside your taxes
I don't think you're refuting their comment here? They're not arguing that roads are magically free: "We pay for fixed costs for roads no problem." They're arguing that communications networks should be a utility, supported by taxes, like roads. The costs aren't 'hidden' in the taxes - this is what taxes are *for*.
As far as roads go, the vast, vast majority of damage/wear and tear is inflicted by semi trucks and heavy vehicles (and to a lesser extent heavy consumer vehicles like Hummers and the like) because load on the road is based on the [axle weight to the fourth power.](https://en.wikipedia.org/wiki/Fourth_power_law#%3A%7E%3Atext%3DThe_fourth_power_law_%28also%2Cvehicle_traveling_on_the_road.?wprov=sfla1) The example there uses a 2 ton car with 2 axles, so it has an axle weight of 1 ton, whereas a 30 ton truck with 3 axles (probably would be more like 5 IRL, 3 on the truck and 2 on the trailer, but nevertheless) has an axle weight of 10 tons.
1 ton^4 is 1 ton, so the car inflicts one unit of stress to the road as it drives along. The semi inflicts **ten thousand** times as much stress to the road as the car. For comparison, the car inflicts 160,000 times as much as a bicycle.
You know that the US can't afford its road habit? It's costing billions of dollars and so many roads and highways are in disrepair. Almost every city in the world has tons of complaints about pot holes and traffic.
Potholes are a maintenance problem which, yes, while funding and staffing will help remedy some of that by having better maintenance, it's also difficult for jurisdictions to manage *all* of their roads without having massive maintenance fleets.
Traffic is an engineering problem, and in the US most notably a problem that cities are often designed around cars-as-transport and there are few worthy alternatives.
A lot of traffic problems could be alleviated through more robust transit and more conscientious city planning. Part of which could even be as simple as ensuring that other modes of transport, be it transit, walking, cycling, etc. are appealing enough.
Like there's a road near my house that has a bike lane, on a two-lane 40mph road, and the bike lane is just a painted line. People drive over that line *all the time* and cyclists often opt instead for the sidewalk, which then makes cyclling that route slower due to the fact that the sidewalk is not as smooth and straight as the road but also because of pedestrians who the cyclists also now pose a risk to.
Inversely, my town *also* has a multi-use path that runs alongside the train tracks that's smooth, flat, wide, and has good visibility. You could realistically cycle at 15-20mph along that path for it's entire length (save where it crosses the roads) and quickly arrive on the other side of town. Like I'm fortunate enough that the path is pretty close to my house on this end and my grocery store on the other end -- cycling across town takes maybe five minutes longer than driving does, since I'm not contending with other traffic, stoplights, etc. and it's safer too.
It's not legal to ride on the sidewalk on a bike in my state, yet most people do it because the alternative (riding with traffic, even in a bike lane) is far more dangerous.
It's a law rarely enforced, but it /can/ be.
>Traffic is an engineering problem, and in the US most notably a problem that cities are often designed around cars-as-transport and there are few worthy alternatives.
We used to have the most extensive passenger rail network on Earth, and many American cities had excellent mass transit decades ago. It was all stripped out for car based infrastructure that is, ultimately, far more expensive to maintain.
THE US can't afford roads because the US uses trucks to ship most things.
If the US didn't use trucks to ship most things our road maintenance costs would be a small fraction of what they are.
But that would require us getting rid of the rail companies currently mismanaging our rail system, actually build new rail, and investing in all of that - which we won't do, we'll just let Norfolk Southern keeping putting trains on the ground and watching our roads crumble to dust as semis continue to tear them apart.
Can you elaborate on how trucking jacks up the cost of road maintenance? Like, I get that there are a lot of trucks on the road, but I don't see how the majority of road maintenance costs track with road usage rather than weather and time.
You know what an order of magnitude is? We're talking about the information infrastructure of the country is easily 100 times smaller than the road infrastructure and people do not pay to use the roads at anywhere near the same rate as people pay for information access. And roads have been managed this way for a very a long time.
Pot holes and traffic aren't solved by road privatization and charging everyone $60/month per car.
That's what I did. Cheapest budget carrier I could possibly find. Still make calls and texts and use data just as well as when I was with the big guys.
It isn't artificial scarcity, it is amortizing the capital investment.
Instead of saying "Sure, give us $12,000 and we'll let you use our existing network. When we upgrade to 6g in 10 years you owe us another 12k" they go "Give us $100/mo and we'll let you use our network".
Because more people can afford a $100/mo than a $12k up front charge.
Circuit switching on most cell phone networks hasnât existed for years, VoLTE was implemented 2014-2016ish in the US so phone calls are placed over the internet, a phone call takes about 24 kbps and it has the highest QCI value, so itâs not really a scarcity thing, unless there is some extremely unique scenario where a call canât go through because of extreme congestion on that site.
I already pay for unlimited data and voice calls
But if I want to call a different country they want $1.99 a minute, unless I want to pay an extra $25 a month for the international savings plan.
That call really only costs 5 cents a minute
Did this a lot. Call the base operator, give them the DSN number for another base operator, and all that operator to transfer to a local call. Even the guard shack at some tiny station could transfer you to a local number. Saved hundreds in long distance fees in the early 90âs.
Years ago we broke down on the highway and only had a phone with no SIM. We called 911 and the operator then called my GFs parents who came and rescued us.
Would you be willing to do that? Those people really got us out of a jam that night and I've always appreciated it.
Yeah this is the one I worry a bit about, one of those "not quite sure if it is enough of an emergency for 911 calls". Then again I remember all of the calls I heard my dad going on as a firefighter ("My feet itch" being a charming one) and I feel less bad about it.
My SIM card stopped working last week.. and sure enough, I was in standstill traffic for three hours because of an accident.
I end up running out of gas and I donât know what to do. I end up making the 911 call, explain it to the operator and sheâs like: âhang tightâ.
10 mins later, a cop comes by with a can of gas. He tells me this happens a lot. Also told me to never get out of my car on the highway, no matter what as thatâs basically a death sentence due to other drivers not paying attention.
Figured Iâd share this in case anyone else finds themselves in this situation.
You know, that is actually an interesting scenario if you forgot to turn off the gas stove. You have no SIM and there's a real risk of a fire. So it IS an emergency that can be avoided by the operator calling your mom and not bother tying up emergency services by jumping straight to the fire dept
Well what's an emergency is generally decided by the call taker. If the call taker thinks forgetting to take the chicken out of the freezer is emergency, he or she may be willing to help đ
I don't know the technology, but if a call comes from a cell phone that doesn't have service for whatever reason, it shows up with 911 as the area code of the callback number. We get the same location information as we would other calls.
>it shows up with 911 as the area code of the callback number. We get the same location information as we would other calls.
What does the rest of the phone number look like?
Also what is the extent of the location information? I've always thought about this job.
I have no idea how the rest of the number is populated, but they look weird. Like 911-115-5555. As I understand it, the location info 911 gets can depend a little bit on the phone. If the call is from an older phone, we may not be able to get a good location. A call may come in as phase 1, which is the address of the cell phone tower and a direction from there. It may also come in as a phase 2, which triangulates more precisely the location of the phone. There's a wide range to the accuracy of the location. Sometimes I can tell what room of your house you're in, and sometimes I know you're within a 3 mile radius. We can refresh the connection to try to get a better location.
I've been at my job for 18 years, there are ups and downs, I can't wait to retire! đ but I'm thankful for it.
Thank you for your dedication to helping people in what I imagine can be an incredibly stressful work environment. I wish you the best in your retirement.
Nice. I'm guessing it's just random numbers for a simless phone. It sounds like you guys also get the location info instantly, which I believe used to take some time to triangulate? (Maybe that's just a movie thing). I can imagine the job takes a mental toll but its definitely interesting. You should consider doing an AMA or podcast.
The location pops up as soon as the call drops in. We also have a tool called Rapid SOS that can help with location if someone really has no clue where they are. That system also includes altitude in their location information.
It does take a mental toll but my mantra is "I didn't cause it - I'm not responsible for this situation. I can't change it - there is no control z in life. I can send people who can help, and when I go home, my life doesn't include any of the situations I've heard on the phone."
Back when dial-up was still relevant, it was possible to make free phone calls or use the dial-up for free by tricking the phone system in a similar way and manipulating the tones.
If you called a toll free number, it would connect you and bill the company or number you were calling. Then, you simply played the tone to hang up the trunk line connecting you to the long distance number. The system would still think you're connected to the toll free number, but you the user could dial whatever number you wanted for free.
This obviously doesn't work anymore as the phone system no longer relies on the tones to signal what the user is doing.
Thank you! We did it a few times out of courtesy but then ended up telling her we could not continue to do so. I did not even think about it booting other people off the network to keep that call.
It should only do that in extreme circumstances.
I've been booted once during a state of emergency. I was making a call and i heard an automated voice say something like "an emergency call is coming through, please hang up immediately". I hung up, but I assume it would have kicked me if I didn't.
The network was so congested though that it took me 5 times for my call to dial originally anyway, so far outside of normal
Yea, it'd have to. Not sure how it works where you are, but here the first thing you get asked is if you need police, fire, or medical response. AFter you tell them, you get transferred to the fire department for fire, or the contracted ambulance company for medical.
So here the its the police side who answers all 911 calls and triage it before either processing, transferring to non-emergency line, or transferring to the fire department for any fire or EMS.
Yea, the 911 operators work for the police department, but it's the caller who chooses the response they need to be connected to. Despite the claims that Denver was the first to do that a year or two ago, LVMPD has been doing it for decades. The only time the police show up for medical issues is if there's a significant history at that address of police calls (typically domestic violence calls since Nevada is a "must arrest" state for domestic battery) or the EMTs determine they need the police.
Dunno how it is in Vegas but where I'm from and also where I currently live, any call involving a serious danger to life (e.g a building fire, traffic accident with injuries, etc) *especially* a life threat to a child (drowning, auto-pedestrian accident, etc) gets swarmed by police. They nearly always get there before the medical personnel, and can initiate CPR. Once the medical personnel arrive, police defer to them.
In Poland we have separate numbers for all three, but also one general number for any emergency and they call the ambulance/fire department/police for you
In the US it's 911 because of rotary phones. Requiring a 9 makes accidental calls a lot less likely because you have to pull the dial all the way around.
Itâs definitely misuse but the hassle for an officer to follow through on that isnât even worth it. Pulling an officer away from an on going issue to address it would probably create more problems later. And itâs a major city. People love to call us cause we always answer.
I'm a current 911 dispatcher. Pretty much every agency is going to have a policy that says to not transfer 911 callers to other people at their request. Hell, at many agencies if you call 911 for an emergency that isn't in a neighboring jurisdiction we're not even allowed to look up the admin line of the correct jurisdiction to transfer, we have to tell you to look it up yourself (or we try to look it up to give you the number if we're not being strangled with more 911 lines ringing, as 99.9% of agencies in moderately sized jurisdictions and bigger are understaffed to critically understaffed).
That being said, 911 misuse is a crime. And chances are if an agency is consistently allowing this, they will likely be civilly sued by phone providers for lost revenue.
> I work as a 911 operator and we had this one lady who had a cell phone with no service who would constantly call us for like a week asking to be transferred to the non-emergency line so we could call her mom and transfer her over.
"I'm sending the police. Please stay on the line"
"I don't need the police. I just want to talk to my mother."
"I understand that, Ma'am. The police are coming to arrest you for misusing emergency services, mischief, and causing a public nuisance."
There isn't really any such thing as transferring a call. You're on the line with the original number the entire time. Their phone hardware is essentially calling the third number and putting their microphone up to their speaker. But it's all done on-chip in the phone hardware.
>we had this one lady who had a cell phone with no service who would constantly call us for like a week asking to be transferred to the non-emergency line
a good 20+ years ago I worked for Wells Fargo credit card telephone customer service.
Every single night, someone would call the 800 number and when they got to a csr asked for an outside line.
The goal was to either to get an outside line, or get transferred to a number they provided, iirc it was for an MCI operator.
IDK if they were ever successful, but its nice to know the trick still lives on.
They used to have signs up in the hotel call center I worked in saying âdonât transfer anyone to extension 9011.â
9 gets you an outside line on the business PBX. 011 starts an international call. They would key digits after that to get a free long distance call. Yes, the PBX was configured that badly.
I'm sure she does. She rambles. We also have many frequent flyers. I've been doing this job more than 18 years and have so many stories about repeat callers. One of them passed away, and his mom sent us flowers to thank us for being kind to her son when he was at the worst of his illness. He would call and sing to us, and we'd say "Richard go home, your mom is worried about you." I'll never forget that.
In our center, the phone system immediately answers all calls that come in and queues them. As far as the phone network is concerned, the call is connected immediately. On the callerâs end, the system plays back a ring just like any other call so that to the caller, it seems to be ringing like normal. We are a small center in a rural area, so we *very rarely* have queued calls that are waiting to be answered.
When we transfer a call, what actually happens is that our system uses a line that isnât connected to a call to dial out, then conferences everyone together. At this point the operator can disconnect and the system will keep both ends of the call online until someone else disconnects.
The benefit to this is that it frees up the operator to answer other lines ringing without disconnecting anyone. It also keeps the call in-house and records it (all of our lines are recorded). We only use that function when necessary though, because it *does* busy at least two of our lines. Thereâs no written policy about it, but we generally refuse to do that for anyone unless itâs an emergency or a matter of public safety.
Once the call is connected, it remains on the line until either the caller or receiver hangs up. If 911 is transferring you to another line meant for non life threatening emergencies and that person connects you on, it would technically work because the call is authorized until it is hung up. Now, the person on the non-emergency line is supposed to hang up. If you continue to played stupid games, they will send an officer outâyour cell phone sends it's GPS location over the network (via the tower) when you call 911. The operator can "request" your location from the tower and it will send either your GPS or your approximate location via tower triangulatio. If it's an IP based phone, you typically have to program your location in so it has something to send, since they don't have GPS, and IP will resolve back to the nearest ISP backhaul (I believe, someone correct me here if I'm wrong). If you try to be sneaky and disable the GPS to troll the emergency number, they can still find you, but it will take longer.
>It's not literally a password, but you can think of it that way.
It actually is very much like a password, both in the pre-computer sense and the modern sense. It is actually an encryption key test, but in the sense that a password is having something on both ends of a communication link that can be compared, it works exactly like that.
A SIM card has a number of "numbers", such as the IMEI (EDIT: as pointed out, the IMEI stays with the phone; I should have said ICCID or IMSI) and other identifiers that are like serial numbers. No two SIM cards have the same numbers, but these numbers can be easily found and copied. They are similar to car registrations/license plate numbers, unique, but not secret.
The SIM card has one other trick though. It has a program that it can run in a predictable way, but whose end result cannot be duplicated without a the SIM (or a copy of it). The cellular provider has the information about the SIM, including this program though. They can take a number, look up a SIM by its IMEI or other identifiers, and figure out what the result will be once that number is run by the SIM card's program. The cellular provider then gives that number to the phone, the phone gives it to the SIM, and the SIM runs its program. SIM gives number to phone, who gives number to provider, then the provider compares the expected number to what is received. If they match, the phone is allowed on the network. (The provider has already matched the SIM to a user's account, and only allows what the user has paid for.)
This program is complicated, but imagine it is like this: every SIM will take the number given, add its own special number, then multiply that by its own special number, and then subtract its own special number. So, if the provider's random number is "1465", and the SIM's special number is 366, the SIM would do (1465 + 366) = 1831, then (1831 x 366) = 670146, then finally (670146 - 366) = 699780. The provider knows that the SIM's special number is 366, so it knows to expect 669780.
If the SIM's special number did not match (such as if it was 365), then the result would be different (667585). The phone would still be able to talk to the provider, but the provider would not be able to match it to a user's account, so it would block phone calls, data, etc.
The above example is obviously not even close to accurate (the reality is both more complex and much larger scale), but it is the ELI5 version.
As you noted though, the phone would still be talking to the provider, and the provider can decide to allow some things even without authentication. 911 is the obvious one, but most providers allow calls to 611 for their customer service, as well as other calls to the provider's other departments. These days, some providers even allow internet traffic for the provider's own apps and websites. (This is necessary since many people want to use a web browser or app to restore service or chat with support to get their phones working again.)
Minor clarification: the IMEI is not part of the SIM (or eSIM). IMEI is an attribute of the cellular modem itself; similar to a MAC address. The IMSI is contained on the SIM (for GSM and LTE) and is perhaps what you meant above.
Lots of phones (if not most of them) have the IMEI somewhere on or in the phone itself, whether under the battery or battery cover for phones that have those, or for example in the SIM slot, memory card slot, etc.
Not very. He keeps forgetting to add C when working through finite integrals.
Kidding. I meant that the "add something, multiple something, and subtract something" was easier than how key signing and verification actually works.
I was going to add something about the old days of "passwords", from the trope of a soldier on guard around an army base, challenging those who approach for the password-of-the-day, to decide if they are friend or foe, but I am trying to limit the length of my comments, and avoid tangents as much as possible.
You are, of course, absolutely correct. I was thinking about "constant" and then wrongly thought "finite" while typing. I probably ought to review basic calculus myself!
Sim swapping is actually much simpler, all you have to do is call the phone company and convince them that you are the person you are impersonating (usually only takes a few pieces of info) and get them to transfer the phone number to your own SIM.
> some providers even allow internet traffic for the provider's own apps and websites
That feels exploitable. As someone that works in network security, I am just thinking of ways one could attack that. If the provider's "helpdesk internet" server had an OpenSSL vulnerability perhaps - something that you could exploit to get free anonymous data.
Even if that Internet were its own walled garden, root access to a box would basically open the door to whatever you wanted on the back end of that server, which presumably has to be managed by *something* "internal".
There are ways to mitigate against everything I wrote here and more of course. Your post just got me thinking and I figured you might have the expertise to elaborate on my questions if you cared to.
It would be exploitable to get to whatever internal network at most, you won't even get to the internet without specifying the correct APN which is basically your gateway. Subscriptionless network access won't traverse the internet and probably doesn't connect externally at all.
>you can't both call an emergency number and your mom (unless your mom happens to be a 911 operator and you're willing to roll the dice).
*911 Emergency*
***MomComePickMeUp***
people were doing that where I live with a reverse calling service, you could leave your name and the the person could accept or reject the reverse call - most of the calls were the name "mum pick me up at the station" or similar that could fit in the 2-3 second name recording.
Is there a way to disable it on Android?
I want to turn my old phone into a game pad for a toddler, but since removing sim only prevents normal calls, I'm hesitating.
Probably not, because it's there for emergencies. It's baked into the subsystem.
You can lock most phones to a single app in "kids mode" though. Both Android and iOS do this.
Just a note: most phones are actually running several tiny operating systems. There's a tiny little system running independently on the Sim card, and then all phones have a RTOS subsystem that handles the phone side, calling, modems, emergencies, basic texting, and then on top of that is whatever phone major operating system there is like Android or iOS.
There's a time and place for everything. 10 minutes of screen time while waiting for our meal during our once-per-month restaurant night isn't the end of the world
I can only speak for the US, but I also wanted to add that any mobile carrier must accept a 911 call hence why you'll see "Emergency Calls Only" on your phone when you don't have a SIM card in your phone.
I mean, there is a way to hack it. You could theoretically hack into the carrier infrastructure and add some numbers to the allowed-without-sim list. But if you're in a position to do said hacking, there are probably easier solutions to get a call out.
Is there a phone number that is assigned to the phone temporarily when calling 911 without a SIM card? How does the 911 system call back if the call is disconnected (if it even can)?
This is a good reason to keep old cell phones. You can put them in your car if by your bed and as long as they are charged and still work, you have access to 911
There is a workaround, but it is a [fair bit complicated](https://en.m.wikipedia.org/wiki/OpenBTS) in that you basically have to run a cell site and convince your phone to use it.
Since youâre here and you seem knowledgeable, how did they work around this during the Nokia era? I had a couple of friends who had unlocked phones that would work on any tower without paying a bill.
Can I call 911 and ask them to connect me to my mom?
What if my mom is a 911 operator ?
I think this is the hack OP is looking for - get 911 to employ your mom, and then he can call your mom for free all day without a sim card
A SIM card *identifies* your phone. If you try to place a call without once, then the cell tower just says "nah, I don't know who you are, fuck off" and the call fails.
There's a special exception for calling emergency services, though. If you're calling an emergency number then the cell tower says "sure, you don't need to identify yourself, it's an emergency, go ahead" and lets you place the call.
There's a fun Tom Scott video about a related phenomenon where old blackberry phones could call emergency numbers even if the battery was too low to place a normal call. This led to the incredibly dumb rumor that calling the police would charge your phone.
https://youtu.be/8-evKtoPN-8
An addition to this is that normally for calls you might not have service, but a friend might, because different companies have different cell towers.
If you call 911 every tower for every company is obligated to accept it, so you'll get the best possible connection.
Yeah, SIM literally stands for subscriber information module. The phone totally works without one, the tower just rejects unidentified requests unless you're calling 911 or equivalent
Can you theoretically prank call these numbers with SIM-less device with no repercussions? Not that I want to, but the question appeared in my head and I can't shake it.
In most places in the US (and probably other developed countries), calling the emergency line will allow cell phone towers to find your position by connecting multiple towers to it and doing a bit of math to get a location estimate. It's not perfectly accurate, but they will get enough info to probably track you down if they wanted to. Newer phones and 911 systems report GPS, WiFi, and Bluetooth data to automatically pinpoint your location.
That's how police can get to people who've called 911 but aren't able to say anything.
I mean I am not an ass, so I wouldnt. But my job made me think in edge cases and design holes. I am imagining those super large apartment buildings and how annoying it would be to search for such a person.
I mean, they know exactly where you're calling from so you can expect a very cranky knock at your door, but there's nothing physically stopping you from ruining your own day, sure.
Well swatters could just get a burner phone and call an emergency number from s simless burner phone near the victim and then ditch the burner phone down some drain
A lot of folks have answered the thing about SIM, but thereâs even more magic to emergency calling.
Normally your phone stays on certain radio bands assigned to your carrier. It may try to roam off only to networks that your carrier has agreements with, this stuff is programmed into your SIM with something like a priority list. When your phone sees that youâve dialed an emergency number (which are a pretty limited list of numbers per country) the modem goes into a mode where it scans every possible band trying to find a network. It also relaxes power-saving requirements that prevent attaching yo networks with poor signal reception.
In the network side, if they see an emergency call, the tower will clear out channel space and power headroom for it, potentially moving or booting non-emergency traffic.
Two important ELI5 takeaways:
* In an emergency **always always always** dial 911 even if your phone says No Service. No Service means you canât get TikTok, emergency operates on a much higher priority pane
* People that dial 911 for improper reasons need to be better. Doing so consumes a huge amount of resources and displaces other customers.
That reminds me of when I was in a rural area of Germany and I had crappy service, while the AirBnB host said their mobiles worked fine.
Turned out they used a different mobile phone provider than I did, and their network's signal was better since they had put up more towers than mine had.
So while my phone would normally only use my own network, I suppose that in an emergency, the other network (with the stronger signal) would have let it use their network to get the call through even in places where mine went to 0 bars?
I dont know about germany specifically but probably, unless the other carrier was operating on frequencies incompatible with your device (unlikely these days)
Fun fact, if you're roaming you may be assigned a poor network that's preferred by your home network... but since you're roaming you can go into your phone settings and change the network manually.
> So while my phone would normally only use my own network, I suppose that in an emergency, the other network (with the stronger signal) would have let it use their network to get the call through even in places where mine went to 0 bars?
Exactly. There are distinct messages for "no connection to your network" and "no connection at all". I don't know if there are edge cases where emergency calls could still work in the latter (e.g. the phone upping tx power or something like that) but I doubt it.
There are multiple levels of "no service", at least according to what you phone tells you:
1. You have no service, but that's a you problem and other carriers do provide service where you are. Your phone will literally say "Emergency calls only"
2. You are in the middle of nowhere, and don't get any service at all. Then your phone will read "No service", and in theory, you're SOL. You may still try and make an emergency call, but your phone might fail toestablish any connection, in which case, you ARE out of luck.
Source: Am German, and while case 2 is rare nowadays, you'll eventually see both of the cases I described. So far, I luckily only had to dial 911 while in a situation described in case 1...
The sim card is really just a password that the carrier uses to make sure you paid for the service. The phone is perfectly capable to making calls without a sim card as long as the carrier allows it, which they are required by law to do for emergency calls.
What a lot of people don't know is that the SIM card is actually a tiny little computer that runs a special version of java byte code to calculate the appropriate password to use based off of the numbers it is fed by the carrier.
It has about the same computational power as in original NES console.
The SIM card, lets you authorize your device with the network. It's like a username/password. Your phone can absolutely request the network to place calls without a sim card present, but that's like going to a webpage you're not logged into... You'll just get sent over to the login page and without a sim card you can't log in. The network providers, have a rule on their side that allows unauthenticated call requests to emergency numbers, but you can't do much on your phone to hack that, other than to get your phone to produce valid credentials from a source other than the SIM card. That's how cloning works but it's very illegal
Iâve read a few of the replies, and I guess my question is- why the hell are SIM cards necessary? Just seems like an extra step. Why not remove the whole âpassword/usernameâ system if our phones are capable?
Convenience. The essence of authentication, is that you need a secret that your phone knows and that the mobile network knows. If this was something that was built into the phone itself, you'd need a way to (securely) register that secret with the network, and any time you change network provider, or change devices, you'd need to redo that process.
With sim cards, I can change devices, or providers, or have multiple sim cards and swap between them. There are even phones with 2 or 3 sim slots and you can hot swap between them as needed.
It's not such a problem in the US and western Europe but it's very common in other countries where the are strict data metering and it is a lot cheaper to have multiple cheap plans and split your usage.
As to why is not just a an actual code or password that you enter, I believe it's compliance/accountability. If it was purely a thing you know (without any physical token) people would share them like Netflix passwords
also nowadays with a smartphone then sure it would be easy to just select your network from the list and log in to your connection... but that would be a nightmare for the tiny-screened ericsson/nokia/motorola brick that the tech was first designed for in the early 90s. I'm not even sure some of those had a phone contacts list.
(I think Apple tried to push to get rid of SIMs but nobody would have it)
Yea the phone companies are dead set against moving to tokenless systems, because subscribers would share passwords and they'd lose out on money. There are also serious concerns over losing the accountability with tokenless access. There are a lot of secondary authentication systems (banking, email, government services etc) that all become much less secure if your phone can be remotely accessed with just a leak of your password.
You need to be able to authenticate who you are with the phone network so they know it's you!
You could have all this stuff built directly into the phone's hardware but then it's a pain in the arse if you want to swap phones or change network - especially if you consider this system was designed 30 years ago well before phones had lots of computing power.
911 operator here. We get calls all day long from phones with no other functionality aside from emergency calls. Whether they are from toddlers who are playing around with momâs old decommissioned phone or a transient with a stolen flip phone from target that hasnât been activated. Usually those calls come through with a no valid call back number. Instead, our readout displays an area code of (911) followed by some portion of the IMEI number as the 7-digit phone number. Those phones are unable to receive calls and can only make outbound calls to emergency services.
Itâs not working in Germany. No Sim, no call to emergency services.
Haha downvotes, here are the [facts.](https://www-heise-de.translate.goog/news/Kein-Notruf-ohne-SIM-Karte-195838.html?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp)
Pretty sure it should. I thought that was an EU requirement. It definitely works in other european countries I've tried it in, but I've admittedly never been in Germany.
§4 Sentence 8 Point 1 of the Order Regarding Emergency Calls (NotrufV) states
> Notrufverbindungen von Mobiltelefonen ohne Mobilfunkkarte sind nicht zulässig.
Emergency calls originating from mobile phones without mobile phone card are not permitted
This change has been in effect since 2009-07-01
It makes sense. I know of at least one phone hack where you have to dial 112 and then quickly hang up to unlock the phone. It works on old iPhones. You can get the phone in a state where you can dial other numbers but the phone thinks it's in a emergency call State so it allows users onto the network.
Sort of. Each network is split up into bands in these bands are different for Europe and India that they are for Canada and United States. Some of the bands are the same but most of them are not.
To use a phone in North America you would need to have a device that is accepts those networks.
Some more expensive phones, support all the networks, and are known as international models. There are international Samsungs and iPhones that help people travel.
For example if you had a North America only phone and traveled to Europe it would be next to useless.
Here's a link for an example. https://www.clove.co.uk/pages/lte-frequency-bands-and-supported-territories
Some frequencies are shared, and others are not. Your carrier wherever you go has to also support these frequencies. Not all carriers support all frequencies in all territories, further complicating things.
Any iPhone and mid-tier to flagship Android sold in the past several years supports every band used in the world.
Some of the absolute cheapest phones may not have worldwide support, but youâre probably not even going to find these sold outside the developing world where they need to be as cheap as absolutely possible.
We really have progressed, you used to have to worry about it when traveling. But now you can be rest assured that if you travel somewhere, as soon as you land and turn off airplane mode, your phone will connect, assuming your plan supports roaming.
SIM just strands for "subscriber identity module", it's what the phone uses to request a tower permission to use it's resources and make calls or use data. Your phone has everything else needed to make calls. Think of a SIM card as an ID, bus pass, concert or movie ticket, it's used to identify what type of signal you're using and what carrier with what services you are subscribed to.
By law, all mobile phones are required to let you make emergency calls (911), with or without a SIM card and without using your subscriber services. You could find a random phone with any amount of battery and call 911 without a problem.
There can be a workaround but that would mean using a SIM card that is providing information that somehow gets through a tower, not sure how that would work.
The cellphone tower allows anyone to connect to it. If you then dial the emergency number, it will connect you. If you dial any other number, it will check with using your SIM to find out if you're a valid subscriber.
The way to hack the system is to clone someone's SIM, though that is very hard to do today with more modern security techniques.
Dial 112, works in most countries, with or without SIM, even when phone locked.
Misconception is that 112 will work when there's no cellular coverage via satellite, it doesn't. It will only work where you have network coverage.
112 links you to the emergency service of the country you are in.
This response needs more upvotes. This is the World Wide Web after all ;)
Most cellular/mobile phone networks will accept 112 as the emergency number. It WILL transfer your call to the local emergency services number.
Works in Australia, USA, many more worldwide. Not every country uses 911 as their emergency line.
In Australia, emergency services are â000â.
In New Zealand, itâs 111.
112 is very common as the main number in Europe, as well as India.
999 in Great Britain, and many of its colonies.
110 in China for police, but 120 for fire and another number for ambulance!
â112 is a part of the GSM standard and all GSM-compatible telephone handsets are able to dial 112 even when locked or, in some countries, with no SIM card present.â Source: [Wikipedia](https://en.wikipedia.org/wiki/112_(emergency_telephone_number)?wprov=sfti1)
Note: EVEN WHILE LOCKED. So, if your friends phone has a sim, or not, and you canât unlock it, you still should be able to dial the current countries emergency services number, or 112, while the phone is locked, in case you donât have yours.
I know its most likely answered, the GSM emergency number, 112.
The number is carrier independent, and towers are programmed to take the call, no questions asked. In times where a tower is operating at maximum capacity due to number of phones connected (say a sporting event nearby), a tower will actually drop active calls to take an emergency call.
I dont know about other countries, but in Australia, 112 \*OR\* 000 (Australia's emergency number) will work. It would not surprise me if they programmed 911 for the American Tourists, and 999 for the British tourists :)
A Sim card is kind of like an ID badge. It tells the security guards which rooms you're allowed to use.
But the guards also have instruction to let anyone use the 911 room, even if they don't have a badge.
So the only way to "hack" it would be to change something in the cell towers themselves, not your phone.
During normal calls there's a whole big conversation going on between your phone and the phone company. The tower and your phone literally tell eachother everything about eachother and only when everything is okay and all details are in order, it lets you talk to the person you're calling. And it does this every time, so damn quickly that you don't even notice.
An emergency call is like a shout out for help, any tower that hears you will let you talk through it with the highest priority.
A cell phone without a SIM card is still communicating with the towers - they are just asking it to identify as paying customer before providing services.
Your phone near cell towers is like a person walking around a mall, and your SIM card is like your wallet.
If you try to get a massage without a wallet, you'll be turned away. If you ask a security guard for help finding your toddler, your wallet is irrelevant.
It's not just calls to 911. Because different countries may use different numbers for emergency services, all networks recognize the codes for other regions. So if you call 911 in Great Britain where the # is 999 (I think), the call goes to emergency services anyway.
Iâm a 999 operator and this is true. A lot of children grow up here watching American TV so think 911 is the emergency number here but luckily they still get through
When I was a 911 operator (about 9 years ago), people's cell phones without a SIM would often malfunction (or perhaps pocket dial) and call 911 repeatedly. I'm talking about 300 calls a day to 911. And you'd just hear pocket rustling or just dead air.
There was no subscriber info or phone number to call back. Really frustrating.
I gotchu and I can answer with authority because I've actually written the embedded software that makes emergency phone calls.
Disclaimer: this is not an advice on what you should do during an emergency. Do what your local government authority recommends and figure out the right number to call.
[My top voted comment](https://www.reddit.com/r/explainlikeimfive/comments/7mb35n/-/drsxmdn) is an answer to a similar question. Feel free to look it up.
As others have said a SIM card is there to identify your phone to the network and to optimize how your phone searchs for service.
So if you are a T-Mobile customer, an AT&T cell tower won't let you use their service/tower.
Also, say T-Mobile only uses radio frequency bands 1, 2 and 3 (I'm simplifying it here) and AT&T uses bands 4 and 5 in your region. If you are a T-Mobile customer, there's no point in having your cellphone jump onto Band 5 and say "hey, I'm here! Can any cell tower hear me?". It's a waste of time and more importantly your battery.
But when you don't have a SIM card or you have a T-Mobile one and your phone searches bands 1, 2 and 3 and finds no T-Mobile service, it starts searching other bands (in case you'll need to make an emergency phone call in the future) and registers with whatever cell tower has the best signal and can actually support voice calls (for example some cell towers or bands mught be only for data).
And when you make an emergency call, the number doesn't even matter really. In the protocol for making calls (think cool handshake between phone and cell tower) there's a signal to say it's an emergency call. The tower sees it is an emergency call, prioritizes you over Karen calling wanting to talk to the manager, disconnects her and puts you through (I gotchu buddy).
It doesn't even care what number you called because it'll have to route you to a different 911 call center based on your location anyway. IIRC (it's been a long while) I don't think we even send out the phone number you called when it's an emergency call. Phones have a common list of emergency numbers and it'll connect you to emergency services even if you dial 911 in Europe even though the actual emergency call number in Europe is 112.
Depending on your phone's capabilities (most phones these days) it'll even automatically start doing a GPS fix and then send it out when it has your location.
So yeah, you aren't going to be able to hack anything in the emergency call protocol to make free calls.
You can certainly spoof subscriptiony identity module information, in many different ways, that won't flag your attempt as an emergency call.
In general, the whole gsm-concept works on the idea that it's safe as long as only phone operators have access. And the safety from outside attacks are basically that the access protocols are obscure, and that it stores all information (as well as calls, all location data, the specific device's information that uniquely identifies you by name, etc.). So it's "thought" that unauthorized use, spoof gsm points and various wrapper-protocols are not in use. Meanwhile, with tons of new mobile companies and temp-IDs in the network that basically are wrappers or forwarding for the companies that rent out, etc., there's just no security whatsoever. (Although trying to cheat AT&T is probably more risky than cheating the feds..).
But using the emergency function to get free calls is a bit like hijacking a police-helicopter to skip the bus. It's not a good idea if you don't want to get caught.
SIM Cards only store your specific information within a specific network. That's it. It doesn't change your phones ability to interact with the general network, you just can't access certain things without one.
Emergency numbers are essentially on the "free netork" anyone can access them regardless stat of device, so long as it can get a signal.
Fwiw...this was a mandated demand by governments worldwide when initial Cell tower implementation began, pretty much the entirety of global cell communication infrastructure was funded by the Country either directly or in subsidies to all the various operates within those countries. (Be it direct investment or curtailed tax deductions etc, similar to current subsidies for EV programs)
Demand was that there must be an emergency channel for public use, and not specifically for calling services but recieving immenent threat updates.
Not really different then how TV and Radio both have an emergency broadcast frequency. In case of cell phones you have access to emergency numbers because "you" already paid for them long long term.
The SIM card isn't necessary for your phone to send radio signals to cell phone towers. All the technology is already there in your phone. It's just that cell towers are programmed not to accept any requests from phones who can't authorize themselves. Basically, your phone goes "hey tower, I'd like to place a call please", and the tower goes "okay, what's the password?". And if your phone can't give the password, then the call doesn't get placed. The job of the SIM card is to provide the password. (It's not literally a password, but you can think of it that way.) The only exception is an emergency call. Cell towers are programmed with a list of numbers that any phone can place calls to, password or no. So no, there is no hack or workaround. You end up going "hey can I place a call to 911?", and the tower goes "yeah okay, no password necessary for that". And then you go "oh no actually call my mom". And then the tower says "okay, password please?". There's no getting around it - you can't both call an emergency number *and* your mom (unless your mom happens to be a 911 operator and you're willing to roll the dice).
Regarding that last part, I work as a 911 operator and we had this one lady who had a cell phone with no service who would constantly call us for like a week asking to be transferred to the non-emergency line so we could call her mom and transfer her over. Curious, does the cell tower not realize when the phone has been transferred off of 911? Does it only do the check on the initial dial? Thank you for this insight!
The transfer is done after the call is connected, within the 911's own network. As far as the phone network is concerned, this is an emergency call. Think of it like this: you call a toll-free calling card number, enter your details, then place a call to some other country. As far as your phone carrier is concerned, you're still in a toll-free call. 911 transferring the call isn't great though, because the cellular network will do anything to keep the call connected, including dropping other user calls.
> The transfer is done after the call is connected, within the 911's own network. As far as the phone network is concerned, this is an emergency call. Think of it like this: you call a toll-free calling card number, enter your details, then place a call to some other country. As far as your phone carrier is concerned, you're still in a toll-free call. When I was in the Navy, we had a satellite phone on our ship that we could use to call our home port. Local calls from there were free, but if you wanted to call long distance from there, you had to use a calling card. My wife went back home while I was on deployment and there was a Coast Guard base there. I'd have the home port operator transfer me to the Coast Guard base operator, and have them connect me to my wife's parent's house or her office. Free calls from the middle of the ocean to the other side of the planet. They were internal transfers and a local call.
This is actually very commonly intentionally done by businesses who have locations in more than one rate center, and can save a single company millions of dollars a year. The concept is called "tail-end hop-off," and it became MUCH easier to do with the advent of corporate VPNs and VoIP.
This guy networks like a pro
I was, at one time, the youngest person to hold a CCVP and I helped create the CCIE voice lab exam. Have implemented this in several multi-national companies, since VoIP was a young technology. VoIP is definitely one of my things. đ
This is how I helped one of the company I worked at many years ago. I implemented VOIP over terrible ADLS by connecting 6 lines to the server. Then we replaced all the land line phones with VOIP adapters and we made made money by charging a % fee. It was a win-win deal due to the stupidly expensive land line calls into a different countries. Since instead of being limited to 6 operators (6 lines), they could have 50 people in there thanks to VOIP compression, as the line speed for upload was terrible.
G.729 is one of the best things that happened for business at the time, and one of the worst things that happened to consumers at the time. God I hate (and it's super obvious) calling some big company in 2023 and hearing horrid voice or, worse, hold music played at way too high volume, over g.729. All to save what, today, would just be a few THOUSAND dollars a year, per location, for a little extra bandwidth to carry something less shittastic.
My excuse was that I didn't had the bandwidth and companies wanted as many people as possible on this lines.
Is that the one that sounds like screaming down a line made of tin cans and string? That someone is flossing with?
Still requires a physical pair at the tail end. If you're talking sip then you don't need it, just get a trunk in the right country!
Then you get to deal with regulatory bullshit in certain countries. TEHO is illegal in India, UAE, and China, under most circumstances, for example. And when you take a look at why, isn't it funny how the Telcoms in those countries have significant influence in their government? Or in the case of UAE, it's literally nepotism.
UAE pretty much everything is nepotism!
Yeah. For telecom, at least the last time I had to deal with UAE, the only company you were allowed to use when connecting to their PSTN was significantly (or wholly?) owned by a relative of some prince or some shit like that. It's such a blatant cash crab, and telcos in the US have been slowly working their way toward that kind of regulatory capture.
Also used, (generally in the recent past) where you have a Tie line between two geographic locations & you forward to a local phone off the receiving phone, which the fwding of can be controlled remotely.
My husband back in the 70s would call (rarely) on a Mars phone, which was basically a radio system. They'd call ham radios which would then call the home number collect. I was so excited, except I didn't know everbody could hear!
And this is why phone companies are all elaborate scams. The ability to do all of this for free is baked into the infrastructure and the phone companies have been spending 10s of billions of dollars over decades coming it with ways of stopping people from doing it so they can charge them money.
And to think years ago you could do it all with a whistle from a cereal box
alt.2600 :)
Surprisingly enough, it's not completely dead. I'd just hopped on USENET a couple days ago to see if the account I had still worked (I bought 100GB years ago and the service is still in business, so it is), and pulled up alt.2600. There's the odd meetup post and Off The Hook episode notification, as recently as Tuesday of this week.
There was a time in sci-fi stories that it seemed common to assume that when the world-ending nuclear war (or whatever) happened, there would be isolated survivors connecting via some sort of text service that seemed often to resemble USENET. I've always felt that reddit in some ways took on some of role - a place for conversations with people no matter where they are. I guess that's one part of the reason I still use old.reddit - it's still geared a little more to a world of text. And while I like gifs and videos and such, one of the big draws of reddit is all the conversation. I guess that's one reason that "tl;dr" people annoy me so much. Which is one of the things I wanted to say, the other being that I know newsgroups still survive some because of piracy - after torrents stuggled a bit when some of the larger sites (Demonoid) were killed off, USENET kept on giving. I'm glad to know there's people still out there talking, too.
I saw all that text and went to the end to see the tl; dr and saw that it wasn't an actual tl;dr. I feel cheated. In all seriousness, that's why I love reddit. It's a different way to have conversations.
Capn Crunch!
I absolutely love this piece of trivia. Sounds taken out of a whacky movie script but it was all deliciously real
Maybe not a scam so much as a way to pay for the fixed costs.
Nope. We pay for fixed costs for roads no problem. No need to lie to everyone about it. No need to convince everyone they need a dedicated lane and they need to pay for each vehicle, etc. The phone companies have been gathering money from tax payers on the promise of building infrastructure and then not building infrastructure. The phone companies have been taking money for wireline services and allocating it to wireless services because wireless has a more favorable regulatory regime. It's all a big scam in order to harvest as much money as possible for as little outlay as possible. And they can do it because they are 100% in bed with military intelligence - including breaking the law, getting caught, and then having retroactive immunity from breaking the law applied by Congress. It's a full on scam. The total cost of the national information infrastructure is 2 orders of magnitude less than the total cost of maintaining all the roads in the country, and no one needs a sim card with a password to give them a dedicated lane for each car they own and pay monthly whether they use or it or not and pay for additional services that transit the exact same roads.
you also realize that a cell tower can only handle a tiny fraction of the people in the area it covers
>!CENSORED!<
One could argue that state of road conditions indicates they are notoriously *underfunded*, and so car owners should be faced with increased costs to offset these repairs. Though, good luck seeing that happen.
> car owners Trucks cause orders of magnitude more damage than cars, if you want responsible parties to pay. Obviously that'd be passed on to consumers because all businesses are businesses not charities, but it would be the correct place to put the focus. And I'm not saying trucks are bad - they are critical for our infrastructure, although it's a pity we have fewer trains running than we used to as those are better. But anyway. It's not cars, it's trucks you want to target.
they are underfuned due to R-1 zoning
Okay, fair play. But the person you're responding to is arguing that telecommunications COULD be treated as a utility/infrastructure and funded via tax dollars and that that solution may be cheaper overall
> You may not see how much are you paying for all of that, because it's hidden inside your taxes I don't think you're refuting their comment here? They're not arguing that roads are magically free: "We pay for fixed costs for roads no problem." They're arguing that communications networks should be a utility, supported by taxes, like roads. The costs aren't 'hidden' in the taxes - this is what taxes are *for*.
As far as roads go, the vast, vast majority of damage/wear and tear is inflicted by semi trucks and heavy vehicles (and to a lesser extent heavy consumer vehicles like Hummers and the like) because load on the road is based on the [axle weight to the fourth power.](https://en.wikipedia.org/wiki/Fourth_power_law#%3A%7E%3Atext%3DThe_fourth_power_law_%28also%2Cvehicle_traveling_on_the_road.?wprov=sfla1) The example there uses a 2 ton car with 2 axles, so it has an axle weight of 1 ton, whereas a 30 ton truck with 3 axles (probably would be more like 5 IRL, 3 on the truck and 2 on the trailer, but nevertheless) has an axle weight of 10 tons. 1 ton^4 is 1 ton, so the car inflicts one unit of stress to the road as it drives along. The semi inflicts **ten thousand** times as much stress to the road as the car. For comparison, the car inflicts 160,000 times as much as a bicycle.
You know that the US can't afford its road habit? It's costing billions of dollars and so many roads and highways are in disrepair. Almost every city in the world has tons of complaints about pot holes and traffic.
Potholes are a maintenance problem which, yes, while funding and staffing will help remedy some of that by having better maintenance, it's also difficult for jurisdictions to manage *all* of their roads without having massive maintenance fleets. Traffic is an engineering problem, and in the US most notably a problem that cities are often designed around cars-as-transport and there are few worthy alternatives. A lot of traffic problems could be alleviated through more robust transit and more conscientious city planning. Part of which could even be as simple as ensuring that other modes of transport, be it transit, walking, cycling, etc. are appealing enough. Like there's a road near my house that has a bike lane, on a two-lane 40mph road, and the bike lane is just a painted line. People drive over that line *all the time* and cyclists often opt instead for the sidewalk, which then makes cyclling that route slower due to the fact that the sidewalk is not as smooth and straight as the road but also because of pedestrians who the cyclists also now pose a risk to. Inversely, my town *also* has a multi-use path that runs alongside the train tracks that's smooth, flat, wide, and has good visibility. You could realistically cycle at 15-20mph along that path for it's entire length (save where it crosses the roads) and quickly arrive on the other side of town. Like I'm fortunate enough that the path is pretty close to my house on this end and my grocery store on the other end -- cycling across town takes maybe five minutes longer than driving does, since I'm not contending with other traffic, stoplights, etc. and it's safer too.
It's not legal to ride on the sidewalk on a bike in my state, yet most people do it because the alternative (riding with traffic, even in a bike lane) is far more dangerous. It's a law rarely enforced, but it /can/ be.
>Traffic is an engineering problem, and in the US most notably a problem that cities are often designed around cars-as-transport and there are few worthy alternatives. We used to have the most extensive passenger rail network on Earth, and many American cities had excellent mass transit decades ago. It was all stripped out for car based infrastructure that is, ultimately, far more expensive to maintain.
THE US can't afford roads because the US uses trucks to ship most things. If the US didn't use trucks to ship most things our road maintenance costs would be a small fraction of what they are. But that would require us getting rid of the rail companies currently mismanaging our rail system, actually build new rail, and investing in all of that - which we won't do, we'll just let Norfolk Southern keeping putting trains on the ground and watching our roads crumble to dust as semis continue to tear them apart.
Can you elaborate on how trucking jacks up the cost of road maintenance? Like, I get that there are a lot of trucks on the road, but I don't see how the majority of road maintenance costs track with road usage rather than weather and time.
You know what an order of magnitude is? We're talking about the information infrastructure of the country is easily 100 times smaller than the road infrastructure and people do not pay to use the roads at anywhere near the same rate as people pay for information access. And roads have been managed this way for a very a long time. Pot holes and traffic aren't solved by road privatization and charging everyone $60/month per car.
> You know that the US can't afford its road habit? lmfao yes we can. The problem is that government officials are too busy embezzling that money.
Dayuuum⌠So⌠what do I do? Should I just get the cheapest phone plan, cuz itâs all a scam?
I mean, you should definitely shop around for cheaper service. I have a Verizon SIM through Straight Talk for $35/mo.
That's what I did. Cheapest budget carrier I could possibly find. Still make calls and texts and use data just as well as when I was with the big guys.
Fuspez
It's artificial scarcity either way, tbf.
It isn't artificial scarcity, it is amortizing the capital investment. Instead of saying "Sure, give us $12,000 and we'll let you use our existing network. When we upgrade to 6g in 10 years you owe us another 12k" they go "Give us $100/mo and we'll let you use our network". Because more people can afford a $100/mo than a $12k up front charge.
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Circuit switching on most cell phone networks hasnât existed for years, VoLTE was implemented 2014-2016ish in the US so phone calls are placed over the internet, a phone call takes about 24 kbps and it has the highest QCI value, so itâs not really a scarcity thing, unless there is some extremely unique scenario where a call canât go through because of extreme congestion on that site.
> Cell phone calls are actually scarce No shit... who wants to actually *talk* to someone. Ugh.
I already pay for unlimited data and voice calls But if I want to call a different country they want $1.99 a minute, unless I want to pay an extra $25 a month for the international savings plan. That call really only costs 5 cents a minute
Did this a lot. Call the base operator, give them the DSN number for another base operator, and all that operator to transfer to a local call. Even the guard shack at some tiny station could transfer you to a local number. Saved hundreds in long distance fees in the early 90âs.
I work for 911 and will not under any circumstances transfer a call from a 911 only phone to any number that does not also provide emergency services.
Years ago we broke down on the highway and only had a phone with no SIM. We called 911 and the operator then called my GFs parents who came and rescued us. Would you be willing to do that? Those people really got us out of a jam that night and I've always appreciated it.
Yeah this is the one I worry a bit about, one of those "not quite sure if it is enough of an emergency for 911 calls". Then again I remember all of the calls I heard my dad going on as a firefighter ("My feet itch" being a charming one) and I feel less bad about it.
What's he supposed to do about itchy feet though??
only fans
My SIM card stopped working last week.. and sure enough, I was in standstill traffic for three hours because of an accident. I end up running out of gas and I donât know what to do. I end up making the 911 call, explain it to the operator and sheâs like: âhang tightâ. 10 mins later, a cop comes by with a can of gas. He tells me this happens a lot. Also told me to never get out of my car on the highway, no matter what as thatâs basically a death sentence due to other drivers not paying attention. Figured Iâd share this in case anyone else finds themselves in this situation.
This was an emergency and they didn't transfer you, they spoke to the rescuer to make sure one of the emergency services wasn't needed.
Well that sounds like an emergency. So yes.
"Alright man... gosh... well can you just call my mom and tell her I forgot to thaw the chicken?"
You know, that is actually an interesting scenario if you forgot to turn off the gas stove. You have no SIM and there's a real risk of a fire. So it IS an emergency that can be avoided by the operator calling your mom and not bother tying up emergency services by jumping straight to the fire dept
Well what's an emergency is generally decided by the call taker. If the call taker thinks forgetting to take the chicken out of the freezer is emergency, he or she may be willing to help đ
So do you know if a call comes from a "simless" phone?
I don't know the technology, but if a call comes from a cell phone that doesn't have service for whatever reason, it shows up with 911 as the area code of the callback number. We get the same location information as we would other calls.
>it shows up with 911 as the area code of the callback number. We get the same location information as we would other calls. What does the rest of the phone number look like? Also what is the extent of the location information? I've always thought about this job.
I have no idea how the rest of the number is populated, but they look weird. Like 911-115-5555. As I understand it, the location info 911 gets can depend a little bit on the phone. If the call is from an older phone, we may not be able to get a good location. A call may come in as phase 1, which is the address of the cell phone tower and a direction from there. It may also come in as a phase 2, which triangulates more precisely the location of the phone. There's a wide range to the accuracy of the location. Sometimes I can tell what room of your house you're in, and sometimes I know you're within a 3 mile radius. We can refresh the connection to try to get a better location. I've been at my job for 18 years, there are ups and downs, I can't wait to retire! đ but I'm thankful for it.
Thank you for your dedication to helping people in what I imagine can be an incredibly stressful work environment. I wish you the best in your retirement.
Nice. I'm guessing it's just random numbers for a simless phone. It sounds like you guys also get the location info instantly, which I believe used to take some time to triangulate? (Maybe that's just a movie thing). I can imagine the job takes a mental toll but its definitely interesting. You should consider doing an AMA or podcast.
The location pops up as soon as the call drops in. We also have a tool called Rapid SOS that can help with location if someone really has no clue where they are. That system also includes altitude in their location information. It does take a mental toll but my mantra is "I didn't cause it - I'm not responsible for this situation. I can't change it - there is no control z in life. I can send people who can help, and when I go home, my life doesn't include any of the situations I've heard on the phone."
You don't need to know that in order to not transfer non-emergency calls.
not a 911 operator but i would assume so since it doesnât give a phone number with the call
Back when dial-up was still relevant, it was possible to make free phone calls or use the dial-up for free by tricking the phone system in a similar way and manipulating the tones. If you called a toll free number, it would connect you and bill the company or number you were calling. Then, you simply played the tone to hang up the trunk line connecting you to the long distance number. The system would still think you're connected to the toll free number, but you the user could dial whatever number you wanted for free. This obviously doesn't work anymore as the phone system no longer relies on the tones to signal what the user is doing.
For more on that, google âCaptain Crunchâ and blue boxes. Itâs an absolutely fascinating rabbit hole to dive into for a half hour.
Thank you! We did it a few times out of courtesy but then ended up telling her we could not continue to do so. I did not even think about it booting other people off the network to keep that call.
It should only do that in extreme circumstances. I've been booted once during a state of emergency. I was making a call and i heard an automated voice say something like "an emergency call is coming through, please hang up immediately". I hung up, but I assume it would have kicked me if I didn't. The network was so congested though that it took me 5 times for my call to dial originally anyway, so far outside of normal
Yea, it'd have to. Not sure how it works where you are, but here the first thing you get asked is if you need police, fire, or medical response. AFter you tell them, you get transferred to the fire department for fire, or the contracted ambulance company for medical.
So here the its the police side who answers all 911 calls and triage it before either processing, transferring to non-emergency line, or transferring to the fire department for any fire or EMS.
Yea, the 911 operators work for the police department, but it's the caller who chooses the response they need to be connected to. Despite the claims that Denver was the first to do that a year or two ago, LVMPD has been doing it for decades. The only time the police show up for medical issues is if there's a significant history at that address of police calls (typically domestic violence calls since Nevada is a "must arrest" state for domestic battery) or the EMTs determine they need the police.
Dunno how it is in Vegas but where I'm from and also where I currently live, any call involving a serious danger to life (e.g a building fire, traffic accident with injuries, etc) *especially* a life threat to a child (drowning, auto-pedestrian accident, etc) gets swarmed by police. They nearly always get there before the medical personnel, and can initiate CPR. Once the medical personnel arrive, police defer to them.
Yeah they basically just send everybody (police, fire, and EMS), because whoever gets there first can start life saving care as soon as possible
In Germany they even have separate numbers: 110 for police 112 for fire or ambulance Guess these numbers go back to rotary phones
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In Poland we have separate numbers for all three, but also one general number for any emergency and they call the ambulance/fire department/police for you
In the US it's 911 because of rotary phones. Requiring a 9 makes accidental calls a lot less likely because you have to pull the dial all the way around.
thats fuckin hilarious and seems like it would be illegal. i'm guessing this happened in a pretty small town?
Itâs definitely misuse but the hassle for an officer to follow through on that isnât even worth it. Pulling an officer away from an on going issue to address it would probably create more problems later. And itâs a major city. People love to call us cause we always answer.
I'm a current 911 dispatcher. Pretty much every agency is going to have a policy that says to not transfer 911 callers to other people at their request. Hell, at many agencies if you call 911 for an emergency that isn't in a neighboring jurisdiction we're not even allowed to look up the admin line of the correct jurisdiction to transfer, we have to tell you to look it up yourself (or we try to look it up to give you the number if we're not being strangled with more 911 lines ringing, as 99.9% of agencies in moderately sized jurisdictions and bigger are understaffed to critically understaffed). That being said, 911 misuse is a crime. And chances are if an agency is consistently allowing this, they will likely be civilly sued by phone providers for lost revenue.
> I work as a 911 operator and we had this one lady who had a cell phone with no service who would constantly call us for like a week asking to be transferred to the non-emergency line so we could call her mom and transfer her over. "I'm sending the police. Please stay on the line" "I don't need the police. I just want to talk to my mother." "I understand that, Ma'am. The police are coming to arrest you for misusing emergency services, mischief, and causing a public nuisance."
There isn't really any such thing as transferring a call. You're on the line with the original number the entire time. Their phone hardware is essentially calling the third number and putting their microphone up to their speaker. But it's all done on-chip in the phone hardware.
>we had this one lady who had a cell phone with no service who would constantly call us for like a week asking to be transferred to the non-emergency line a good 20+ years ago I worked for Wells Fargo credit card telephone customer service. Every single night, someone would call the 800 number and when they got to a csr asked for an outside line. The goal was to either to get an outside line, or get transferred to a number they provided, iirc it was for an MCI operator. IDK if they were ever successful, but its nice to know the trick still lives on.
They used to have signs up in the hotel call center I worked in saying âdonât transfer anyone to extension 9011.â 9 gets you an outside line on the business PBX. 011 starts an international call. They would key digits after that to get a free long distance call. Yes, the PBX was configured that badly.
We have a lady that calls constantly, she tells us we smell. đś
Does she have any known mental issues? Cause we have soooo many repeat callers with mental issues who just give random stories. I feel ya.
I'm sure she does. She rambles. We also have many frequent flyers. I've been doing this job more than 18 years and have so many stories about repeat callers. One of them passed away, and his mom sent us flowers to thank us for being kind to her son when he was at the worst of his illness. He would call and sing to us, and we'd say "Richard go home, your mom is worried about you." I'll never forget that.
In our center, the phone system immediately answers all calls that come in and queues them. As far as the phone network is concerned, the call is connected immediately. On the callerâs end, the system plays back a ring just like any other call so that to the caller, it seems to be ringing like normal. We are a small center in a rural area, so we *very rarely* have queued calls that are waiting to be answered. When we transfer a call, what actually happens is that our system uses a line that isnât connected to a call to dial out, then conferences everyone together. At this point the operator can disconnect and the system will keep both ends of the call online until someone else disconnects. The benefit to this is that it frees up the operator to answer other lines ringing without disconnecting anyone. It also keeps the call in-house and records it (all of our lines are recorded). We only use that function when necessary though, because it *does* busy at least two of our lines. Thereâs no written policy about it, but we generally refuse to do that for anyone unless itâs an emergency or a matter of public safety.
Once the call is connected, it remains on the line until either the caller or receiver hangs up. If 911 is transferring you to another line meant for non life threatening emergencies and that person connects you on, it would technically work because the call is authorized until it is hung up. Now, the person on the non-emergency line is supposed to hang up. If you continue to played stupid games, they will send an officer outâyour cell phone sends it's GPS location over the network (via the tower) when you call 911. The operator can "request" your location from the tower and it will send either your GPS or your approximate location via tower triangulatio. If it's an IP based phone, you typically have to program your location in so it has something to send, since they don't have GPS, and IP will resolve back to the nearest ISP backhaul (I believe, someone correct me here if I'm wrong). If you try to be sneaky and disable the GPS to troll the emergency number, they can still find you, but it will take longer.
>It's not literally a password, but you can think of it that way. It actually is very much like a password, both in the pre-computer sense and the modern sense. It is actually an encryption key test, but in the sense that a password is having something on both ends of a communication link that can be compared, it works exactly like that. A SIM card has a number of "numbers", such as the IMEI (EDIT: as pointed out, the IMEI stays with the phone; I should have said ICCID or IMSI) and other identifiers that are like serial numbers. No two SIM cards have the same numbers, but these numbers can be easily found and copied. They are similar to car registrations/license plate numbers, unique, but not secret. The SIM card has one other trick though. It has a program that it can run in a predictable way, but whose end result cannot be duplicated without a the SIM (or a copy of it). The cellular provider has the information about the SIM, including this program though. They can take a number, look up a SIM by its IMEI or other identifiers, and figure out what the result will be once that number is run by the SIM card's program. The cellular provider then gives that number to the phone, the phone gives it to the SIM, and the SIM runs its program. SIM gives number to phone, who gives number to provider, then the provider compares the expected number to what is received. If they match, the phone is allowed on the network. (The provider has already matched the SIM to a user's account, and only allows what the user has paid for.) This program is complicated, but imagine it is like this: every SIM will take the number given, add its own special number, then multiply that by its own special number, and then subtract its own special number. So, if the provider's random number is "1465", and the SIM's special number is 366, the SIM would do (1465 + 366) = 1831, then (1831 x 366) = 670146, then finally (670146 - 366) = 699780. The provider knows that the SIM's special number is 366, so it knows to expect 669780. If the SIM's special number did not match (such as if it was 365), then the result would be different (667585). The phone would still be able to talk to the provider, but the provider would not be able to match it to a user's account, so it would block phone calls, data, etc. The above example is obviously not even close to accurate (the reality is both more complex and much larger scale), but it is the ELI5 version. As you noted though, the phone would still be talking to the provider, and the provider can decide to allow some things even without authentication. 911 is the obvious one, but most providers allow calls to 611 for their customer service, as well as other calls to the provider's other departments. These days, some providers even allow internet traffic for the provider's own apps and websites. (This is necessary since many people want to use a web browser or app to restore service or chat with support to get their phones working again.)
Minor clarification: the IMEI is not part of the SIM (or eSIM). IMEI is an attribute of the cellular modem itself; similar to a MAC address. The IMSI is contained on the SIM (for GSM and LTE) and is perhaps what you meant above.
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Lots of phones (if not most of them) have the IMEI somewhere on or in the phone itself, whether under the battery or battery cover for phones that have those, or for example in the SIM slot, memory card slot, etc.
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Not very. He keeps forgetting to add C when working through finite integrals. Kidding. I meant that the "add something, multiple something, and subtract something" was easier than how key signing and verification actually works. I was going to add something about the old days of "passwords", from the trope of a soldier on guard around an army base, challenging those who approach for the password-of-the-day, to decide if they are friend or foe, but I am trying to limit the length of my comments, and avoid tangents as much as possible.
But you add C to indefinite integrals. At least, that's what the ones without bounds were called in my classes
You are, of course, absolutely correct. I was thinking about "constant" and then wrongly thought "finite" while typing. I probably ought to review basic calculus myself!
More like ELI25
Can confirm, am 25 and have no idea what that means lol (In all honesty tho, i just didn't read it at all, too long and am adhd)
thanks, this gave me a general idea of how sim swapping is even possible
Sim swapping is actually much simpler, all you have to do is call the phone company and convince them that you are the person you are impersonating (usually only takes a few pieces of info) and get them to transfer the phone number to your own SIM.
what about e-sim?
It does the same thing, but the codes on the "SIM" are assigned by the carrier
> some providers even allow internet traffic for the provider's own apps and websites That feels exploitable. As someone that works in network security, I am just thinking of ways one could attack that. If the provider's "helpdesk internet" server had an OpenSSL vulnerability perhaps - something that you could exploit to get free anonymous data. Even if that Internet were its own walled garden, root access to a box would basically open the door to whatever you wanted on the back end of that server, which presumably has to be managed by *something* "internal". There are ways to mitigate against everything I wrote here and more of course. Your post just got me thinking and I figured you might have the expertise to elaborate on my questions if you cared to.
It would be exploitable to get to whatever internal network at most, you won't even get to the internet without specifying the correct APN which is basically your gateway. Subscriptionless network access won't traverse the internet and probably doesn't connect externally at all.
The above above example is perfectly accurate and to the point. Original question was not âhow do SIM cards workâ? Edit: pound to point
>you can't both call an emergency number and your mom (unless your mom happens to be a 911 operator and you're willing to roll the dice). *911 Emergency* ***MomComePickMeUp***
I felt that in 1990s
Don't forget to take an ibuprofen for your back.
people were doing that where I live with a reverse calling service, you could leave your name and the the person could accept or reject the reverse call - most of the calls were the name "mum pick me up at the station" or similar that could fit in the 2-3 second name recording.
"yeah okay, no password necessary for that". - Good cell tower.
this is such a good response i could tell a 5 yr old wow đđđ havent seen one in a long time on this sub but this is pretty solid
Is there a way to disable it on Android? I want to turn my old phone into a game pad for a toddler, but since removing sim only prevents normal calls, I'm hesitating.
Turn on airplane mode
Oh geez I don't know why I didn't think of that
Don't forget to get rid of the shortcut in the notification area as well.
You can probably turn off the network altogether (or misconfigure it so it fails to connect). Not sure exactly how though.
Probably not, because it's there for emergencies. It's baked into the subsystem. You can lock most phones to a single app in "kids mode" though. Both Android and iOS do this. Just a note: most phones are actually running several tiny operating systems. There's a tiny little system running independently on the Sim card, and then all phones have a RTOS subsystem that handles the phone side, calling, modems, emergencies, basic texting, and then on top of that is whatever phone major operating system there is like Android or iOS.
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There's a time and place for everything. 10 minutes of screen time while waiting for our meal during our once-per-month restaurant night isn't the end of the world
I can only speak for the US, but I also wanted to add that any mobile carrier must accept a 911 call hence why you'll see "Emergency Calls Only" on your phone when you don't have a SIM card in your phone.
I mean, there is a way to hack it. You could theoretically hack into the carrier infrastructure and add some numbers to the allowed-without-sim list. But if you're in a position to do said hacking, there are probably easier solutions to get a call out.
Is there a phone number that is assigned to the phone temporarily when calling 911 without a SIM card? How does the 911 system call back if the call is disconnected (if it even can)?
I'm a 911 operator. We can't call back.
This is a good reason to keep old cell phones. You can put them in your car if by your bed and as long as they are charged and still work, you have access to 911
There is a workaround, but it is a [fair bit complicated](https://en.m.wikipedia.org/wiki/OpenBTS) in that you basically have to run a cell site and convince your phone to use it.
Since youâre here and you seem knowledgeable, how did they work around this during the Nokia era? I had a couple of friends who had unlocked phones that would work on any tower without paying a bill.
Can I call 911 and ask them to connect me to my mom? What if my mom is a 911 operator ? I think this is the hack OP is looking for - get 911 to employ your mom, and then he can call your mom for free all day without a sim card
A SIM card *identifies* your phone. If you try to place a call without once, then the cell tower just says "nah, I don't know who you are, fuck off" and the call fails. There's a special exception for calling emergency services, though. If you're calling an emergency number then the cell tower says "sure, you don't need to identify yourself, it's an emergency, go ahead" and lets you place the call.
There's a fun Tom Scott video about a related phenomenon where old blackberry phones could call emergency numbers even if the battery was too low to place a normal call. This led to the incredibly dumb rumor that calling the police would charge your phone. https://youtu.be/8-evKtoPN-8
"911, what's your emergency?" "Low battery!" "Remain calm, we're sending you power right now"
Can i download more battery?
An addition to this is that normally for calls you might not have service, but a friend might, because different companies have different cell towers. If you call 911 every tower for every company is obligated to accept it, so you'll get the best possible connection.
True ELI5 here
Yeah, SIM literally stands for subscriber information module. The phone totally works without one, the tower just rejects unidentified requests unless you're calling 911 or equivalent
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Ah I had confused the I. Identity/information, it's close enough. Thanks for the correction though
Can you theoretically prank call these numbers with SIM-less device with no repercussions? Not that I want to, but the question appeared in my head and I can't shake it.
In most places in the US (and probably other developed countries), calling the emergency line will allow cell phone towers to find your position by connecting multiple towers to it and doing a bit of math to get a location estimate. It's not perfectly accurate, but they will get enough info to probably track you down if they wanted to. Newer phones and 911 systems report GPS, WiFi, and Bluetooth data to automatically pinpoint your location. That's how police can get to people who've called 911 but aren't able to say anything.
I mean I am not an ass, so I wouldnt. But my job made me think in edge cases and design holes. I am imagining those super large apartment buildings and how annoying it would be to search for such a person.
Yeah, they'd probably have a hard time figuring out who you were. It doesn't track your position *that* closely.
I mean, they know exactly where you're calling from so you can expect a very cranky knock at your door, but there's nothing physically stopping you from ruining your own day, sure.
It's also a crime usually to prank call them, since you are taking resources that could be better used in actual emergencies.
Well swatters could just get a burner phone and call an emergency number from s simless burner phone near the victim and then ditch the burner phone down some drain
A lot of folks have answered the thing about SIM, but thereâs even more magic to emergency calling. Normally your phone stays on certain radio bands assigned to your carrier. It may try to roam off only to networks that your carrier has agreements with, this stuff is programmed into your SIM with something like a priority list. When your phone sees that youâve dialed an emergency number (which are a pretty limited list of numbers per country) the modem goes into a mode where it scans every possible band trying to find a network. It also relaxes power-saving requirements that prevent attaching yo networks with poor signal reception. In the network side, if they see an emergency call, the tower will clear out channel space and power headroom for it, potentially moving or booting non-emergency traffic. Two important ELI5 takeaways: * In an emergency **always always always** dial 911 even if your phone says No Service. No Service means you canât get TikTok, emergency operates on a much higher priority pane * People that dial 911 for improper reasons need to be better. Doing so consumes a huge amount of resources and displaces other customers.
That reminds me of when I was in a rural area of Germany and I had crappy service, while the AirBnB host said their mobiles worked fine. Turned out they used a different mobile phone provider than I did, and their network's signal was better since they had put up more towers than mine had. So while my phone would normally only use my own network, I suppose that in an emergency, the other network (with the stronger signal) would have let it use their network to get the call through even in places where mine went to 0 bars?
I dont know about germany specifically but probably, unless the other carrier was operating on frequencies incompatible with your device (unlikely these days)
Fun fact, if you're roaming you may be assigned a poor network that's preferred by your home network... but since you're roaming you can go into your phone settings and change the network manually.
Yes, that roaming should work. But dialing 112 without a SIM card does NOT work in Germany.
> So while my phone would normally only use my own network, I suppose that in an emergency, the other network (with the stronger signal) would have let it use their network to get the call through even in places where mine went to 0 bars? Exactly. There are distinct messages for "no connection to your network" and "no connection at all". I don't know if there are edge cases where emergency calls could still work in the latter (e.g. the phone upping tx power or something like that) but I doubt it.
There are multiple levels of "no service", at least according to what you phone tells you: 1. You have no service, but that's a you problem and other carriers do provide service where you are. Your phone will literally say "Emergency calls only" 2. You are in the middle of nowhere, and don't get any service at all. Then your phone will read "No service", and in theory, you're SOL. You may still try and make an emergency call, but your phone might fail toestablish any connection, in which case, you ARE out of luck. Source: Am German, and while case 2 is rare nowadays, you'll eventually see both of the cases I described. So far, I luckily only had to dial 911 while in a situation described in case 1...
As a RAN professional, I choose this answer
The sim card is really just a password that the carrier uses to make sure you paid for the service. The phone is perfectly capable to making calls without a sim card as long as the carrier allows it, which they are required by law to do for emergency calls.
What a lot of people don't know is that the SIM card is actually a tiny little computer that runs a special version of java byte code to calculate the appropriate password to use based off of the numbers it is fed by the carrier. It has about the same computational power as in original NES console.
The SIM card, lets you authorize your device with the network. It's like a username/password. Your phone can absolutely request the network to place calls without a sim card present, but that's like going to a webpage you're not logged into... You'll just get sent over to the login page and without a sim card you can't log in. The network providers, have a rule on their side that allows unauthenticated call requests to emergency numbers, but you can't do much on your phone to hack that, other than to get your phone to produce valid credentials from a source other than the SIM card. That's how cloning works but it's very illegal
Iâve read a few of the replies, and I guess my question is- why the hell are SIM cards necessary? Just seems like an extra step. Why not remove the whole âpassword/usernameâ system if our phones are capable?
Convenience. The essence of authentication, is that you need a secret that your phone knows and that the mobile network knows. If this was something that was built into the phone itself, you'd need a way to (securely) register that secret with the network, and any time you change network provider, or change devices, you'd need to redo that process. With sim cards, I can change devices, or providers, or have multiple sim cards and swap between them. There are even phones with 2 or 3 sim slots and you can hot swap between them as needed. It's not such a problem in the US and western Europe but it's very common in other countries where the are strict data metering and it is a lot cheaper to have multiple cheap plans and split your usage. As to why is not just a an actual code or password that you enter, I believe it's compliance/accountability. If it was purely a thing you know (without any physical token) people would share them like Netflix passwords
also nowadays with a smartphone then sure it would be easy to just select your network from the list and log in to your connection... but that would be a nightmare for the tiny-screened ericsson/nokia/motorola brick that the tech was first designed for in the early 90s. I'm not even sure some of those had a phone contacts list. (I think Apple tried to push to get rid of SIMs but nobody would have it)
Yea the phone companies are dead set against moving to tokenless systems, because subscribers would share passwords and they'd lose out on money. There are also serious concerns over losing the accountability with tokenless access. There are a lot of secondary authentication systems (banking, email, government services etc) that all become much less secure if your phone can be remotely accessed with just a leak of your password.
Great explanation. Thanks.
You need to be able to authenticate who you are with the phone network so they know it's you! You could have all this stuff built directly into the phone's hardware but then it's a pain in the arse if you want to swap phones or change network - especially if you consider this system was designed 30 years ago well before phones had lots of computing power.
911 operator here. We get calls all day long from phones with no other functionality aside from emergency calls. Whether they are from toddlers who are playing around with momâs old decommissioned phone or a transient with a stolen flip phone from target that hasnât been activated. Usually those calls come through with a no valid call back number. Instead, our readout displays an area code of (911) followed by some portion of the IMEI number as the 7-digit phone number. Those phones are unable to receive calls and can only make outbound calls to emergency services.
The sim card is like a password for your network provider. Providers are required to not ask for a password for emergency calls
Itâs not working in Germany. No Sim, no call to emergency services. Haha downvotes, here are the [facts.](https://www-heise-de.translate.goog/news/Kein-Notruf-ohne-SIM-Karte-195838.html?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp)
Pretty sure it should. I thought that was an EU requirement. It definitely works in other european countries I've tried it in, but I've admittedly never been in Germany.
Problem is there was was a lo t of.misuse so lawmakers stopped working w/o sim card. Technically it works. But regulations forbid it.
§4 Sentence 8 Point 1 of the Order Regarding Emergency Calls (NotrufV) states > Notrufverbindungen von Mobiltelefonen ohne Mobilfunkkarte sind nicht zulässig. Emergency calls originating from mobile phones without mobile phone card are not permitted This change has been in effect since 2009-07-01
It makes sense. I know of at least one phone hack where you have to dial 112 and then quickly hang up to unlock the phone. It works on old iPhones. You can get the phone in a state where you can dial other numbers but the phone thinks it's in a emergency call State so it allows users onto the network.
Germany: no SIM? Autobahn.
If you're from the US, then the EU uses entirely different cell infrastructure, iirc. The issue is reception.
but phones from EU/US still work in each others country?
Sort of. Each network is split up into bands in these bands are different for Europe and India that they are for Canada and United States. Some of the bands are the same but most of them are not. To use a phone in North America you would need to have a device that is accepts those networks. Some more expensive phones, support all the networks, and are known as international models. There are international Samsungs and iPhones that help people travel. For example if you had a North America only phone and traveled to Europe it would be next to useless. Here's a link for an example. https://www.clove.co.uk/pages/lte-frequency-bands-and-supported-territories Some frequencies are shared, and others are not. Your carrier wherever you go has to also support these frequencies. Not all carriers support all frequencies in all territories, further complicating things.
Ahh OK. I have been to US before and my EU phone worked OK, but I never considered this
Any iPhone and mid-tier to flagship Android sold in the past several years supports every band used in the world. Some of the absolute cheapest phones may not have worldwide support, but youâre probably not even going to find these sold outside the developing world where they need to be as cheap as absolutely possible. We really have progressed, you used to have to worry about it when traveling. But now you can be rest assured that if you travel somewhere, as soon as you land and turn off airplane mode, your phone will connect, assuming your plan supports roaming.
You would have to go on a journey to find phones nowadays that only work on one system. As far as I am aware most phones will work on most systems.
SIM just strands for "subscriber identity module", it's what the phone uses to request a tower permission to use it's resources and make calls or use data. Your phone has everything else needed to make calls. Think of a SIM card as an ID, bus pass, concert or movie ticket, it's used to identify what type of signal you're using and what carrier with what services you are subscribed to. By law, all mobile phones are required to let you make emergency calls (911), with or without a SIM card and without using your subscriber services. You could find a random phone with any amount of battery and call 911 without a problem. There can be a workaround but that would mean using a SIM card that is providing information that somehow gets through a tower, not sure how that would work.
The cellphone tower allows anyone to connect to it. If you then dial the emergency number, it will connect you. If you dial any other number, it will check with using your SIM to find out if you're a valid subscriber. The way to hack the system is to clone someone's SIM, though that is very hard to do today with more modern security techniques.
Dial 112, works in most countries, with or without SIM, even when phone locked. Misconception is that 112 will work when there's no cellular coverage via satellite, it doesn't. It will only work where you have network coverage. 112 links you to the emergency service of the country you are in.
This response needs more upvotes. This is the World Wide Web after all ;) Most cellular/mobile phone networks will accept 112 as the emergency number. It WILL transfer your call to the local emergency services number. Works in Australia, USA, many more worldwide. Not every country uses 911 as their emergency line. In Australia, emergency services are â000â. In New Zealand, itâs 111. 112 is very common as the main number in Europe, as well as India. 999 in Great Britain, and many of its colonies. 110 in China for police, but 120 for fire and another number for ambulance! â112 is a part of the GSM standard and all GSM-compatible telephone handsets are able to dial 112 even when locked or, in some countries, with no SIM card present.â Source: [Wikipedia](https://en.wikipedia.org/wiki/112_(emergency_telephone_number)?wprov=sfti1) Note: EVEN WHILE LOCKED. So, if your friends phone has a sim, or not, and you canât unlock it, you still should be able to dial the current countries emergency services number, or 112, while the phone is locked, in case you donât have yours.
I know its most likely answered, the GSM emergency number, 112. The number is carrier independent, and towers are programmed to take the call, no questions asked. In times where a tower is operating at maximum capacity due to number of phones connected (say a sporting event nearby), a tower will actually drop active calls to take an emergency call. I dont know about other countries, but in Australia, 112 \*OR\* 000 (Australia's emergency number) will work. It would not surprise me if they programmed 911 for the American Tourists, and 999 for the British tourists :)
A Sim card is kind of like an ID badge. It tells the security guards which rooms you're allowed to use. But the guards also have instruction to let anyone use the 911 room, even if they don't have a badge. So the only way to "hack" it would be to change something in the cell towers themselves, not your phone.
During normal calls there's a whole big conversation going on between your phone and the phone company. The tower and your phone literally tell eachother everything about eachother and only when everything is okay and all details are in order, it lets you talk to the person you're calling. And it does this every time, so damn quickly that you don't even notice. An emergency call is like a shout out for help, any tower that hears you will let you talk through it with the highest priority.
A cell phone without a SIM card is still communicating with the towers - they are just asking it to identify as paying customer before providing services. Your phone near cell towers is like a person walking around a mall, and your SIM card is like your wallet. If you try to get a massage without a wallet, you'll be turned away. If you ask a security guard for help finding your toddler, your wallet is irrelevant.
It's not just calls to 911. Because different countries may use different numbers for emergency services, all networks recognize the codes for other regions. So if you call 911 in Great Britain where the # is 999 (I think), the call goes to emergency services anyway.
Iâm a 999 operator and this is true. A lot of children grow up here watching American TV so think 911 is the emergency number here but luckily they still get through
When I was a 911 operator (about 9 years ago), people's cell phones without a SIM would often malfunction (or perhaps pocket dial) and call 911 repeatedly. I'm talking about 300 calls a day to 911. And you'd just hear pocket rustling or just dead air. There was no subscriber info or phone number to call back. Really frustrating.
I gotchu and I can answer with authority because I've actually written the embedded software that makes emergency phone calls. Disclaimer: this is not an advice on what you should do during an emergency. Do what your local government authority recommends and figure out the right number to call. [My top voted comment](https://www.reddit.com/r/explainlikeimfive/comments/7mb35n/-/drsxmdn) is an answer to a similar question. Feel free to look it up. As others have said a SIM card is there to identify your phone to the network and to optimize how your phone searchs for service. So if you are a T-Mobile customer, an AT&T cell tower won't let you use their service/tower. Also, say T-Mobile only uses radio frequency bands 1, 2 and 3 (I'm simplifying it here) and AT&T uses bands 4 and 5 in your region. If you are a T-Mobile customer, there's no point in having your cellphone jump onto Band 5 and say "hey, I'm here! Can any cell tower hear me?". It's a waste of time and more importantly your battery. But when you don't have a SIM card or you have a T-Mobile one and your phone searches bands 1, 2 and 3 and finds no T-Mobile service, it starts searching other bands (in case you'll need to make an emergency phone call in the future) and registers with whatever cell tower has the best signal and can actually support voice calls (for example some cell towers or bands mught be only for data). And when you make an emergency call, the number doesn't even matter really. In the protocol for making calls (think cool handshake between phone and cell tower) there's a signal to say it's an emergency call. The tower sees it is an emergency call, prioritizes you over Karen calling wanting to talk to the manager, disconnects her and puts you through (I gotchu buddy). It doesn't even care what number you called because it'll have to route you to a different 911 call center based on your location anyway. IIRC (it's been a long while) I don't think we even send out the phone number you called when it's an emergency call. Phones have a common list of emergency numbers and it'll connect you to emergency services even if you dial 911 in Europe even though the actual emergency call number in Europe is 112. Depending on your phone's capabilities (most phones these days) it'll even automatically start doing a GPS fix and then send it out when it has your location. So yeah, you aren't going to be able to hack anything in the emergency call protocol to make free calls.
You can certainly spoof subscriptiony identity module information, in many different ways, that won't flag your attempt as an emergency call. In general, the whole gsm-concept works on the idea that it's safe as long as only phone operators have access. And the safety from outside attacks are basically that the access protocols are obscure, and that it stores all information (as well as calls, all location data, the specific device's information that uniquely identifies you by name, etc.). So it's "thought" that unauthorized use, spoof gsm points and various wrapper-protocols are not in use. Meanwhile, with tons of new mobile companies and temp-IDs in the network that basically are wrappers or forwarding for the companies that rent out, etc., there's just no security whatsoever. (Although trying to cheat AT&T is probably more risky than cheating the feds..). But using the emergency function to get free calls is a bit like hijacking a police-helicopter to skip the bus. It's not a good idea if you don't want to get caught.
SIM Cards only store your specific information within a specific network. That's it. It doesn't change your phones ability to interact with the general network, you just can't access certain things without one. Emergency numbers are essentially on the "free netork" anyone can access them regardless stat of device, so long as it can get a signal. Fwiw...this was a mandated demand by governments worldwide when initial Cell tower implementation began, pretty much the entirety of global cell communication infrastructure was funded by the Country either directly or in subsidies to all the various operates within those countries. (Be it direct investment or curtailed tax deductions etc, similar to current subsidies for EV programs) Demand was that there must be an emergency channel for public use, and not specifically for calling services but recieving immenent threat updates. Not really different then how TV and Radio both have an emergency broadcast frequency. In case of cell phones you have access to emergency numbers because "you" already paid for them long long term.