There are apps that allow maps to be uploaded, but I haven't tried them as yet. I still rely on "real" GPS units for my navigation - both on the road and off ... in addition to paper maps.

I have a friend (actually my son's Scoutmaster) who works for a recently purchases mobile phone company. I asked him about the details of GPS location on smart phones, and he pretty much said what Doug just said. They have GPS chip sets AND have the ability to triangulate via cell towers using signal strength to provide pretty good location without the GPS chip.

I lost my faith in the smart phone navigation when this Scoutmaster missed several turns on the way up to summer camp because his smart phone lost signal (or at least "hesitated" in its updating) just before the turns came up. My Garmin Nuvi simply does not do that.

My previous Nuvi had a tendency to reboot spontaneously and ultimately refused to start up one evening ... in downtown Detroit ... in the pouring rain ... with the battery in my smart phone almost dead. Sigh. Luckily my smart phone had enough power to get me back up onto the highway - where at least I knew where I was. I bought a new Nuvi on the way home the next morning.