1. A wireless end-user device comprising: a wireless wide area network (WWAN) modem to communicate data for Internet service activities between the device and at least one WWAN, when configured for and connected to the WWAN; a wireless local area network (WLAN) modem to communicate data for Internet service activities between the device and at least one WLAN, when configured for and connected to the WLAN; memory configured to store a WWAN network access policy to be applied when the wireless end-user device communicates or attempts to communicate over the at least one WWAN, the WWAN network access policy comprising one or more first policy instructions associated with a first software application of a plurality of software applications resident on the device, and not with a second software application of the plurality of software applications; and one or more processors configured to implement an application service interface agent to identify network data traffic flows with respective tag information, the tag information associating a responsible one of the plurality of software applications with each identified network data traffic flow, a network stack to provide the plurality of software applications with Internet data access through the WWAN and WLAN modems, the network stack comprising elements including a network service Application Programming Interface (API) accessible by the plurality of software applications to request Internet service activities, an Internet Protocol (IP) socket management function to manage IP sockets for the requested Internet service activities, and respective modem drivers for the WWAN and WLAN modems, at least one of the network stack elements accessing the tag information to identify a first network traffic flow that is associated with the first software application, the at least one of the network stack elements applying the one or more first policy instructions to the first network traffic flow.