The average cellular phone is capable of doing a lot more than just being set up for service and used the way the cellular providers intend them to be.
Most cell phones have a test mode, where special functions can be accessed.
This allows cellular fraud to happen. This information is broadcast from the phone and picked up by the cell tower. The cell tower computer system then cross checks the pair with valid customers and will allow access or refuse access depending upon on the result of the verification. Now since all this information is passing back and forth in the radio spectrum, and no encryption is being used to protect the information, anyone can simply listen in on the proper frequencies and record other people's ESN and MIN codes. Once a valid pair is obtained, it can be reprogrammed into a different cellular phone.