A multi-mode mobile station includes a first interface for wireless communication with a wireless local area network (WLAN) and a second interface for wireless communication with a wireless wide area network (WWAN). An internetwork service control system controls how services are provided to the multi-mode mobile station via the WLAN and the WWAN. The same service logic in the internetwork service control system can control the provision of services via both the WLAN and the WWAN. For example, a service logic module can be executed to define SIP signaling to control the provision of a service via the WLAN and can be executed to define WIN signaling to control the provision of the same service via the WWAN. The internetwork service control system may also include a call state monitor that maintains the call state of the multi-mode mobile station via the WLAN and the WWAN.