A location mapping service (“LMS”) that allows the integrations of an IMS core with the location-based billing methods of a legacy core network. The LMS uses the estimated location of a mobile device during an IMS session in order to determine a Cell Global Identification (“CGI”) to associate with the session. The LMS then provides the determined CGI to the legacy core network, so that a billing gateway may determine the billing region to associate with the IMS session. The LMS thereby facilitates location-based billing for IMS sessions in the absence of actual CGI information.
