Apparatus, and an associated method, facilitates authentication of a mobile station operable in a 3G cellular communication system having a core network and a plurality of access networks. A standard signaling protocol is used to communicate between an access network and the core network. When a request for authentication of a mobile station is generated, a signaling protocol message is generated at a proxy of the access network within which the mobile station is to be authenticated. Detection of the authentication request is made at the proxy, and a message is generated at the proxy which includes indicia associated with the authentication center associated with the access network. The signaling protocol message is sent to the core network, and the information indicia contained therein is used to facilitate authentication procedures to authenticate the mobile station.