To use a cellular phone, you need to subscribe to a wireless service provider. When a phone number is assigned and the cellular phone is programmed, all the information needed for the phone and system to work together is entered into the cellular phone.
The phone is designed to look for a wireless signal and keep on looking until it finds one. When a cellular phone is turned on, it listens to the information that is constantly broadcast by the wireless carrier in what is called an overhead signal. The phone then matches the overhead signal to the signal identification code in the phone. If they match, your phone rings with the incoming call.