A wireless end-user device has WWAN and WLAN modems. A memory stores a WWAN network access policy specific to data traffic usage and/or attempted usage by a first software application but not a second software application. An application service interface agent identifies network data traffic flows with respective tag information that associates a responsible one of a plurality of software applications with each identified network data traffic flow. One or more elements of a network stack then use the tag information to identify a network data traffic flow associated with the first software application, the one or more elements applying the network access policy to the identified network data traffic flow.