My cell phone number has an area code that is different (like, several hundred miles different) from the area code of the place I live. If I called 911 from my phone, would I be connected to a dispatcher back in the old area code, or is it worked out that I’d be connected to someone local? If the former, how would I call for local emergency help - by dialing the local area code and then 911?
You get the local 911 center no matter where you call from. It would not make sense to do anything else since so many people travel outside their home area.
I actually just talked about this with a Battalion Chief at our local fire department.
Right now (in northeast Ohio anyway) the calls from a cell phone are routed to a regional dispatcher who then routes it to someone local. But a system is in the works where your location would be extracted using the nearest cell phone tower that your call is being placed through. The call would then be routed to a dispatcher closer to your actual location.
I believe this is all under the blanket of what is known as E911
Mostly the answer to your 911 call is determined by which cell tower your call is placed through.
In the central Calif bay area a 911 cell call goes to the CHP dispatcher in Vallejo, Ca who will redirect it. There was a plan to have the cell towers determine if you were on a state highway, local streets, or stationary then direct the call to the correct dispatch station.
I can answer from experience. I once witnessed an accident in Greensboro, NC, and called 911 from my cell phone with an Illinois area code. Got right through to a local dispatcher and the authorities were on hand almost immediately. The system works!
One snag to the system, which is well described by the above posters, is when you get close to state lines. Apparently, the MA/NH border is a problem around here, and often calls from one side of the border go to the state police call centers in the other state. I think they have a mechanism to deal with it once a live person is on both ends of the phone, but it is a delay.
Something worth noting about GSM phones. The phone doesn’t actually know what its number is. Your mobile number is something your provider’s network knows about, and it maps it to the International Mobile Subscriber Identity (IMSI) in the SIM card. It is the IMSI that the GSM network uses to find your handset, and it is the IMSI that the networks see when you make a call. The IMSI allows the network to find your provider and negotiate access and billing information. Finding the dialable mobile number requires that the network you are currently making a call on ask your provider’s system to tell it. One would assume that at this point an emergency services system would understand the uselessness of an area code that merely maps to the area where your provider’s system resides.