1. A mobile end-user device comprising: a cellular data modem configurable to connect to one or more wireless wide area data networks; a wireless data modem configurable to connect to one or more wireless local area data networks; a stored access network policy for one or more specific applications stored on the device and executable by the device, the access network policy including a classification for at least one of the specific applications as to whether or not that application is allowed to initiate access network communication activity when the application is running as a background application and the mobile end-user device is connected to at least one data network via at least one of the cellular data modem and the wireless data modem; and at least one agent configurable to enforce the stored access network policy for access network communication activity by one of the specific applications when that application is running, based at least in part on a determination as to whether or not the running application is running as a background application.