A telephony interface system has a controller and multiple communication interfaces to provide voice-over-packet (VoP) telephone service with PSTN telephone service as backup. The telephony interface system has a communication interface for at least one telephony device, a communication interface for the PSTN, and a communication interface for a packet-switched network. To originate a call, the telephony interface system connects the telephony device to the PSTN if the dialed digits for the call correspond to a predetermined telephone number or numbers, such as 911. Otherwise, the telephone interface system connects the telephony device to the packet-switched network.