The big difference between cell phone GPS and dedicated GPS, is that the dedicated GPS's come preloaded with the maps. The cell phones have to load the maps from the network as needed. They both use GPS satellites to establish location. The cell phone can also use WiFi signals, internet IP adresses, and cell tower signals to approximate it's location in liu of a GPS, sometimes with really off results.

There are cell phone GPS applications intended for off road use, and don't require a network connection of any type. The one I currently favor is "GPS Test Plus" by Chartcross. It gives you bearing and distance to a point. Repeatability is about 50 ft. "Waypoint Pro" is a little more powerfull, being able to show bearing and heading to multiple points simultaneously. But, the bearing can get badly skewed by the emmisions from the dashboard electronics and the steel (magnetic)car frame.