For hunting purposes I use my phone and tablet as a GPS. As already stated you do not need cellular connections to use the GPS on your phone and I usually have mine turned off so the phone isn't wasting battery looking for a connection in remote areas. You do have to have the maps stored on your phone for the GPS to show you were you are.
The two programs I am familiar with are Back Country Navigator and Delorme's Earth Mate app. I am sure there are more travel orientated map data bases out there but for what I do I want forest, BLM and landowner maps as well as Arial photo's. Currently I have about 7 GB of map data on my 32 GB SD cards in both my phone and tablet which covers about 5 hunting areas. The thing is I have a general road and topo map downloaded for the whole US but if I want any detail maps I have to download these maps while I have WIFI or burn data to down load over cellular and if I missed a map or change plans I just might not have the maps I need.
I do find using the earth mate app when in the back country and the google map when on the highways keeps me covered and I haven't had any problems. Generally while on the main roads I know were I'm going and just hook up my old Tom Tom for general direction and mileage information.