They don't (well, some do, but 911 can't use it).they say that cell phones have a gps chip in them so the location is known for 911 calls. I think they should program this chip to detect motion and if it detects greater than 5 mph the key pad of the phone locks
Actually, you may be thinking of years ago, when E-911 was first mandated. Ths Link for example gives a relatively thorough description of GPS enabled phones these days. Without a GPS enabled phone, triangulation may be attempted but is pretty much guaranteed to not be accurate, especially in areas where techinical "gotchas", such as multipath, can easily have you routedin very strange ways.They don't (well, some do, but 911 can't use it).
The location is triangulated from signal strength between cellphone relay antennas.