I use my iPhone every time I go on a road trip (every week). I have found the Google Maps app to be very useful when in an unfamiliar area, so you know roads, short cuts, etc and don't get lost.
However, I have found that you shouldn't rely on apps to tell you where EVERY bank is, they always miss a few it seems. In fact there are 2 banks within 10 miles of my house that don't show up at all. I always map out my road trips the day before, using multiple sources to find banks. Sometimes that means going to each bank's website and writing down all of their locations. One of my best scores on a road trip (4 solid rolls of silver) came from a bank that never showed up on any search. Quite a miracle I found it completely by accident. So yes iPhones are very useful (just like a GPS) but don't rely on it 100%... you have to do your research first.
Good luck and HH!
~Syrys