Your comments are correct for phones that relay on cell tower for location determination.
The Andriod phones have a true gps receiver, so the lack of cell tower coverage doesn't limit their useability for nav purposes (or for mountain hiking...). I understand the new, maybe more recent iPhones also now have a true gps. Although I have milspec Casio clamshell which has been an excellent phone - waterproof - after a buddy tracked the progress of last Sunday's thunderstorms to a T with his iPhone weather radar app, I feel that functionality is a must have...especially if you are sailing a smaller boat.
I need to figure out whether an Android is good enough, or even better...
all iphones for sale today have true gps. the 3g,3gs and 4 all have it. Only the first gen didn't and you cant get them anymore except maybe ebay.