Disclosed is a home zone service method for assigning a specified zone to a mobile telephone subscriber and charging the subscriber at different billing rated accordingly as the subscriber makes a telephone call inside or outside the zone. The system includes a mobile device, a first network, and a second network. The gear includes a plurality of teeth each having a thickness in a central plane of the gear and a lesser thickness towards both sides of the gear, so that a gap is defined between the teeth is larger towards both sides of the gear than in the central plane of the gear.