The invention provides systems, including a methods and apparatus, for providing seamless telephone service across MSC's that support multiple or different protocols. In accordance with a preferred embodiment of the invention, the home mobile switching center, where the subscriber record is stored, is equipped to respond to a first inquiry signal from an originating mobile switching center by identifying itself to the originating mobile switching center. The incoming call may then be trunked to the home mobile switching center and forwarded to the visited mobile switching center according to the second protocol. According to another preferred embodiment, in response to the first inquiry signal, the home mobile switching center sends a second inquiry signal to the visited mobile switching center. The first inquiry signal represents a request for an identification number identifying, in the first protocol, the visited mobile switching center. The second inquiry signal represents a request for an identification number identifying in the second protocol, visited mobile switching center. In response to the second inquiry signal, the visited mobile switching center returns a first response signal to the home mobile switching center. In response to the first response signal, the home mobile switching center sends a second response signal to the originating mobile switching center, the second response signal representing, in the first protocol, a number identifying the visited mobile switching center. The call is then directly routed from the originating mobile switching center to the visited mobile switching center.