A digital telephone switch allows transparent switching from a convention telephone service to a cable digital telephone service. The switch is connected to the customer premises equipment and to the old and new telephone services. In its initial state, the switch connects the customer premises equipment to the old telephone service, leaving the new telephone service disconnected. Once a ring is detected on the new telephone service, or another appropriate control signal is received, the switch disconnects the customer premises equipment from the old telephone service and connects the customer premises equipment to the new telephone service. One embodiment can switch back and forth between the old and new telephone services to accommodate intercoms and the like.