I have a 10" tablet which has no 3g connection at all. I can put it in airplane mode and the GPS still works. Also, in the Google Maps app you can download sections of maps to a local cache so they work when disconnected from WIFI (basically ANY networking). So the same should be true for a phone. The specific Android implementation and phone's controls may or may not allow it.

As already mentioned the OsmAnd app is a fairly full featured GPS app with down loadable maps.