The dual registration system tracks two serving Mobile Switching Centers for each subscriber. The registrations are differentiated as IP Multimedia Subsystem for voice call delivery purposes and CDMA Mobile Switching Center for IP access and other non-voice services. The registration message from the IP Multimedia Subsystem is enhanced via protocol extensions to include an indication that this registration is from the IP Multimedia Subsystem and is to indicate the target Mobile Switching Center for IP Multimedia Subsystem services, such as VoIP. The Home Location Register is enhanced to store two Mobile Switching Centers as the serving Mobile Switching Centers for the dual mode subscriber. The Home Location Register logic is extended to route service to the appropriate Mobile Switching Center depending on service offered, subscriber preferences, and the registration status.