not true...with an iphone atleast. You're right about the triangulation with cell service, but the gps chip in the iphone will still provide you with a location and use of a gps app.
I live in a rural area myself and have an app that i use (motion x gps) to do my traking, and there are places with no cell service that the gps chip still operates and creates the track. Then when i get home i can upload it to my topousa map!
The iphone apps that I've looked at are still not any better then a handheld gps unit, but is a cheaper way to go if you've already got the phone. Still have an issue with little battery life however.