Abstract: An electronic prepay adapter circuit is provided for use in converting semi-postpay central office telephone equipment to operation in a full prepay mode. In one arrangement, a prepay adapter circuit is connected on a line by line basis between each pay station and the associated line relay of the central office telephone equipment. In another arrangement, the prepay adapter circuit is connected between the linefinder and the first selector of the central office telephone equipment and utilized on a common or shared basis for a plurality of pay station telephone lines. The prepay adapter circuit is easily connected as a self-contained unit or module into the central office telephone equipment by the connection of the central office battery supply, ringing generator, collect and return voltage supplies, sleeve control lead, and the tip and ring line connections.