A novel method of and system for enabling the use of one portable cellular phone only in voice communication over a radio voice channel with a cellular network control center for voice-requesting position or location data or other services; and, with the aid of a vehicle GPS-transpoder activated in response to signaling from the control center over a separate radio-data channel path, to receive and process at the vehicle GPS location,data from satellites, and to transmit the location data over the said data control path to the control center; and for then sending such data and information therefrom to the user of the portable cellular phone—the system being also adaptable for use by dispatcher managers of fleets of vehicles.