I have used various types of GPS units for over ten years, and they certainly can be very helpful. They are in no sense a substitute for a decent paper map of the area in which you may be navigating. I have not seen a consumer grade GPS with anything like the detail I would like to see for backcountry hiking, or even four wheeling on dirt roads. Even with a GPS, you will still need traditional map reading/route finding skills.

What does work nicely are topo maps on CD-ROMs that interact with your GPS. This adds a laptop to your kit, but if you are dragging around a satellite phone, what the hell? I prefer to print out a paper copy of the area I am going into, and download critical waypoints into my GPS beforehand.