An address management method is provided, for use when a mobile terminal accesses a service from a WLAN access network, wherein the service is provided in a 3GPP network or in a service provider network via the 3GPP network. First, the mobile terminal connects to the WLAN access network. Second, the mobile terminal sends a tunnel setup request message from the WLAN access network to a network entity located in the 3GPP network, wherein the tunnel setup request message includes a service request identifier for accessing a requested service and a mobile terminal identifier. Third, the network entity receives the tunnel setup request message, and allocates an address for use by the mobile terminal to access the requested service based on the service request identifier and the mobile terminal identifier.