Abstract: A payment system utilizing a payment card (5) is employed for a telephone set (1) which forms part of the general telephone network and is connected to a telephone central office (2) via a subscriber's line (3). The telephone set and the telephone central office are provided with first devices which exchange first signals via the subscriber's line. The first devices include first subsidiary devices for identification of the payment card (5) concerned, second subsidiary devices for sensing of the residual value (5a) on the card, and third subsidiary devices for erasure and possible indication of the residual value on the card after this has been used for calls subject to a charge. The payment system also serves an installation separate from the telephone system, which can comprise an automatic parking installation. The letter includes a parking meter (14) and this and the telephone central office are provided with second devices which exchange second signals via the subscriber's line (3).