A mechanism to permit the cryptographic authentication of a mobile device in the cellular carrier's network when the device is present in the 802.11 network, wireless LAN, served by a Cellular Controller and not connected directly to the cellular carrier's network via a radio link is disclosed. The Cellular Controller acts as a proxy for the mobile device when the device is in a building served by an 802.11 wireless LAN. The solutions features the separation of a mobile device's radio function from its ANSI-41 authentication mechanism to permit the proxy function to work and to not have to duplicate the ANSI-41 authentication data and CAVE algorithm.