Disclosed is a device in an IP Multimedia Subsystem (IMS) that provides IMS services to terminating non-IP (TNIP) devices. The method includes receiving a message to register a Public User Identity (PUID) at a TNIP device at a network-based device, the TNIP device being at an E.164 routing address, establishing, in a network device accepting communications where to send sessions destined for a PUID and providing information where to send sessions, the routing address as a final destination of sessions to the PUID based on the registration and an IP address of a network device with routing functionality based on telephone numbers as immediate destinations and using information from the registration to route to the TNIP device, after providing IMS services, using the relationship between the PUID, the routing address and the IP address of the network device with routing functionality based on telephone numbers.