A multimedia terminal adapter for a "data over cable" system includes a host processor. A network interface may be coupled to a cable modem termination system via a cable transceiver. The adapter includes a plurality of device ports. An applications platform is executed on the host processor for providing standardized application program interfaces for allowing compliant application programs to access network services via the network interface to provide multimedia content to at least one of the device ports. A SIP proxy is provided for responding to interconnection of a SIP-compatible device to one of the device ports and for intermediating access to SIP-based services via the network interface.