Mobile voice communications technology has enjoyed substantial growth over the past decade. Many cars, trucks, airplanes, boats, and other vehicles are equipped with devices that allow convenient and reliable mobile voice communications using a network of satellite-based or land-based transceivers. Advances in this technology have led to widespread use of portable mobile units, such as hand-held or vehicle-mounted cellular telephones, for voice communications. Demands for further advances include mobile voice communications technology capable of supporting personal and enhanced services, such as emergency assistance and vehicle monitoring, locating, and tracking.