Abstract: In various embodiments, a mobile device connected to a cellular network performs a credential exchange with a telephone not connected to an Internet Protocol (IP) network. The mobile device relays, via the cellular network, registration information between the telephone and a telephony interconnect service, based in part on the credential exchange. The mobile device receives an indication of a telephone call associated with a user of the mobile device. The mobile device proxies, via the cellular network, the telephone call between the telephony interconnect service and the telephone.