Method for billing pre-paid multi-services

Method for computing a quota of service time or service volume requested by a user (10) in a system wherein a service provider (12) is adapted to provide a plurality of services to the user having pre-paid an amount of money on a user account in order to access at least one service. This method comprises the steps of determining whether the product of the amount of money (AMOUNT) by a reserved part (PART) is greater than a predetermined minimum reserve of money (MIN-RESERVE), and computing the quota which is equal to the minimum (MIN1) of the product and a maximum quantity of service (MAX-FLAT) that the user may reserve while being in a flat rate interval divided by the cost of one unit of the requested service (RATE) if the product is greater than said predetermined minimum reserve of money or to the minimum (MIN2) of the amount of money, the maximum quantity of service and the minimum reserve of money, divided by the cost of one unit of the requested service (RATE) if the product is less than the minimum reserve of money.