JRed is right..... the county/jurisdiction where the 911 cell phone call was made has to buy the technology to be able to triangulate it. Our municipality has it. If someone calls 911 from a cell phone and hangs up, the technology can triangulate the location and give us a general area (about 2 blocks or so) where the call originated from. Now, we get dispatched to that location, but that doesn't mean the caller is always still there.
On top of all this, the phone call has to be made from a Phase 2 cell phone, which provides the ability to BE triangulated (GPS signals and whatnot). Most cell phones these days are Phase 2.... even the "phone in a box" phones. Problem with those is that they can't RECEIVE calls. So if dispatch tries to call that number back, it won't go through.
Going back to what Mr TV said, I'd also be afraid to commit a crime not just because people could call 911 from their phone, but because they could also take pictures and video of you committing the crime. You see it all the time, except the phones are used to record cops tasing people instead of the people committing a crime.
