The Masterphone System uses existing service provider infrastructure to determine that a cell phone is in a moving vehicle. It also determines when two or more phones are in the same vehicle. If it only detects a single phone in a vehicle, texting is disabled for that phone until it drops below a velocity threshold for a set amount of time. If the system detects multiple phones in the same vehicle, it looks for one of the phones to be registered as a Masterphone. The Masterphone is disabled for texting, and the other phones in the vehicle are allowed to text. So, if a driver wants his passengers to text, he registers his phone – typically by a 1-button speed dial or by a voice activated call. Otherwise, no one in the vehicle can text.