In one embodiment a router connects to a cellular network using at least one authentication credential stored on a smart card of the router. The router receives, from a client device coupled to the router, a Session Initiation Protocol (SIP) request to register with an Internet Protocol Multimedia Subsystem (IMS) network coupled to the cellular network. The router sends a SIP registration request for the client device to the IMS network, the SIP registration request comprising authorization information associated with the router, wherein the authorization information associated with the router is used by the IMS network to register the client device with the IMS network.