Systems and methods for measuring and reporting prepaid service usage are provided. More particularly, monitoring and reporting packet data session usage for purposes of charging for service usage are provided. In some embodiments, layer-3 data packet monitoring is used to determine usage. In other embodiments, the start and end of a packet data session are used to determine usage. The usage can be determined from the duration of the packet data session or from the size or amount of packets sent and received by a mobile node.