Abstract: An ability to hold a record of amount of funds prepaid for at the point of the sale is incorporated within a subscriber identity module (or "SIM") of a mobile radio terminal. This payment record will progressively decrease as services of the network are used according to tarif rate which is either preprogrammed in to the SIM or sent by the network. The SIM monitors the remaining value of the payment and, when the value of the payment reaches a predetermined minimum value, prevents further calls. This blocking of the mobile station may be effected by a specific blocking command outputted to a mobile equipment part of the mobile station, or by disabling network operation functions, such as authentication algorithms, in the SIM, or by not sendind a specific acknowledgement to the network.