A method (300) for carrier network integration through a user proxy interface includes receiving a request (130) from a mobile device (110) associated with a subscriber (10) of a carrier provider (301) to establish voice services with the carrier provider for a companion device (120) linked to the mobile device. The request includes a subscriber identifier (132) of the mobile device. The method also includes authenticating the companion device based on the subscriber identifier, obtaining session initiation protocol (SIP) credentials (140) corresponding to the subscriber identifier, and registering the SIP credentials for the companion device at a network interface proxy (200). The network interface proxy is in communication with an internet protocol multimedia subsystem (IMS) (320) of the carrier provider and the companion device. The method also includes establishing voice services between the companion device and the IMS through the network interface proxy using the SIP credentials.