The Wherifone combines GPS and GSM technologies. When you do a location request, the Wherifone will reference a system of 24 GPS satellites circling the earth. At the same time, the Wherifone taps into the GSM network based on the location of the closest GSM cell tower to narrow down the search window for GPS signals. This significantly shortens the time it takes to get a GPS reading. In addition, in places where GPS signal strength is weak, such as inside a concrete building or an underground parking structure, Wherifys Location Service Center will fall back on GSM cell tower location. This way, the Wherifone is equipped to get a location reading regardless of GPS signal strength. The Wherifone must have GSM network coverage, however, to work.