A system and method to allow call traffic localization within a mobile switching center server pool (MSS pool) or between MSS pools, provides a trunk group identifier mapped to an originating media gateway. An originating mobile switching center server (MSC server) initiates a call session with a terminating MSC server by sending a session initiation protocol (SIP) message that includes a trunk group identifier mapped to an originating media gateway identity. The terminating MSC server examines the mapping received in the SIP message, and uses the trunk group identifier to select a terminating media gateway for call routing to realize call traffic localization.