The invention relates to the control of billing in a communications network. The objective is to accomplish a mechanism for minimizing credit losses caused by subscribers, while at the same time maintaining good performance of the system. A gateway receives service requests and filters out the requests for which the analysis performed indicates that a credit loss risk is involved. For these service requests an in-advance credit check is initiated. If the credit check indicates that the delivery is permissible, a reservation is made for the amount of money corresponding to the service price, i.e. the said sum is reserved in the subscriber account so that said sum cannot be used by another service request in the meantime. When the service has been delivered successfully, the reservation is confirmed and the said sum is debited from the balance of the subscriber account. Otherwise, the reservation is cancelled.