Be aware that if you take it off roading all of the jarring could break the internals. A phone is fine for street use but the screen/internals might break if you take it off road. I've done it, luckily it was under warranty since my phone cost $600.

 

I use my iphone as a GPS in town for quick directions. I mounted a netbook and hooked to my Garmin 60csx for tracking and offroad. Garmin runs off satellite, phone off towers.

 

I use Motion X GPS app, it was a few dollars. It is has a lot of features, you can enter lat and lon, maps and data can be stored, all the basics and you can download maps while you are on the network so it can be used where no cell signal is available.

 

Motion X here as well... after purchasing it, there is no fee unless you want it to talk to you.

 

I use the geocaching.com app as well. I think it workks really well!