An analog interface (20) providing POTS device operation from a subscriber premises private exchange (28) connected to a digital network includes an input connected to a ringing signal supply having a DC offset, wherein the input is selectively connected to the ring lead of an analog port (58, 64). A switch is coupled to the input and to the ring lead for selectively connecting the ringing signal to the ring lead. A sensor is coupled across the impedance, the sensor detecting no DC signal during ringing generation when a POTS subscriber terminal is on-hook. However, the sensor detects a DC signal across the impedance when the subscriber terminal device is off-hook. Thus, the sensor detects ring trip and is coupled to a switch in order to disconnect the input lead from the ring lead wherein ring trip is detected.