I've been using the free app Trimble Outdoors Navigator on my 3GS. Works pretty well, though it seems to have a problem tracking a car at freeway speeds.

Anybody tried this app? What do you think of it?

Does anyone know if Trimble Outdoors Navigator PRO is available for the iPhone? Supposedly that one will save maps, which I can't get the free one to do.

I'm curious, too, about just how the location function works. Does it run only from GPS data, or does it somehow also try to figure out its location from WiFi reception?