The invention relates to a road toll system using a vehicle-mounted satellite navigation receiver, from which routes taken and road prices incurred are determined. A billing system bills a user in dependence on the road prices incurred. A portable activation device transmits information concerning the owner of the portable activation device to the vehicle-mounted unit, and the vehicle-mounted unit provides information to the billing system to enable identification of the owner of the portable activation device.In combination, the portable activation device and the vehicle-mounted unit can be considered to function in a similar way to a known vehicle-mounted OBU. However, by separating the data necessary to provide user-personalization into the portable activation device, the vehicle-mounted unit can become more standard, and the user is able to drive other vehicles more easily.