1. A method of operation within a network system comprising one or more network elements, the method comprising: receiving a first usage measure from a mobile end-user device, the first usage measure specifying the mobile end-user device's use of one or more network data services over a mobile access network and corresponding to a first data usage classification; obtaining a second usage measure based on one or more measurements taken within the mobile access network and/or the network system, the second usage measure specifying the mobile end-user device's use of the one or more network data services over the mobile access network and corresponding to a second data usage classification, the second data usage classification being different than the first data usage classification; and synchronizing the first and second usage measures, the synchronization including adjusting at least one of the first usage measure and the second usage measure to account for a difference between the first data usage classification and the second data usage classification.