An apparatus for converting a distinctive ring to a selective ring includes a rectifier connected between a main telephone line and ancillary telephone lines to prevent AC ring current from passing to the ancillary lines. A relay is connected to each ancillary line with contacts connecting the ancillary line to the rectifier. Each relay has additional contacts to which the ancillary telephone lines may be selectively connected, the additional contacts being connected to the main telephone line, bypassing the rectifier. When a selected relay is energized, ring current bypasses the rectifier and will ring the telephone on that ancillary line. A cadence detecting circuit includes a "quiet" interval measuring circuit and an "active" interval measuring circuit, to measure the first "ring" and the first "quiet" interval between rings. The quiet interval circuit will energize one relay if the quiet interval is less than a predetermined length. The active interval circuit will energize a different relay if the active interval is of a minimum length of time.