FIELD: automatic data communications using prepayment card. SUBSTANCE: code number of card is set up of two groups of digits of which first one is card number and second group is identification number of random sequence of digits; computer system output is effected according to card number and code number of card is identified by computer system of communication station according to card identification number by reading out digits in arbitrarily chosen order, choice of subscriber number, output to computer system, and identification of card being made concurrently. Proposed invention is easy to implement. EFFECT: improved system protection against unauthorized data access, enhanced reliability, and efficiency. 2 cl, 2 dwg
