Although most modern cellphones have global positioning system transceivers in them, GPS units do not have a dedicated phone number assigned to them. GPS units operate on an entirely different principle.
GPS units receive their signals from a network of 24 GPS satellites that orbit the Earth. The position of three satellites relative to the device determines the location of the device through a mathematical process called trilateration. A fourth satellite provides time relativity to adjust for the delays in measurement due to the time it takes for the signals to travel miles through the air. This service was established by the U.S. government and was made available for civilian use in the 1980s.