Abstract: A cellular phone system in which a cellular phone user (CPU) has a cellular phone with a predetermined amount of available airtime. The CPU prepays for a particular number of airtime units. When a cell site receives a call from the CPU, the cell site communicates with a mobile telecommunications switching office (MTSO), which recognizes a unique serial number from the cellular phone. The MTSO directs the call to a prepaid airtime transaction tracking interface (PATTI). The PATTI then checks whether the CPU's account has any available airtime units and may indicate the number of units to the CPU. If none, the PATTI does not answer the call; otherwise, the PATTI connects the call and deducts airtime units until the call is disconnected.