What Happens When Making A Call?

Scan Control Channels: Your cell phone needs to use the "closest" base station because that's the one with the strongest signal and the one that will give the best connection. To find the closest base station, your phone checks all 21 control channels and determines which has the strongest signal.

Choose Strongest: Your cell phone chooses the strongest signal and decides to use that one for placing the call.

Send Origination Message: Your cell phone now transmits a very short message (about 1/4 second) that contains the MIN (Mobile Identification Number, aka your cell phone number), its ESN (Electronic Serial Number), and the number you just dialed.

Get Channel Assignment: After the cellular service provider verifies that you are a valid, paying customer (based on the MIN and ESN your phone sent), the base station sends a Channel Assignment message to your phone (also a short 1/4-second burst). This message tells your phone where (that is, on which channel) the conversation will take place.

Begin Conversation: Your cell phone tunes to the assigned channel and begins the call. The spurts you hear that indicate the phone is ringing at the other end (which is called "ring back") or the busy signal that you hear do not begin until you get to this step. Both of these are transmitted by the base station as an audio signal just like the voice of the person you are calling.

For more information, check out: How Do Cell Phones Work?