I travel with the Google Droid. Same exact thing, different OS. I've been on the road with it for 6 months now.
I'm sure you have some sort of Maps/Google Maps equivalent on there. I can't tell you HOW MANY times this app has saved my ass in tight spots.
I was hungry and alone in Atlanta, Ga. I google mapped the nearest grocery stores to dumpster.
My road dogs and I were lost in Mississippi, we google mapped our way out and to the highway.
People (dirty kids and crustlords) will give you shit for it, mainly because they feel it's "cheating". But whatever. It's a phone and a tool just like any other. The means don't matter as much as the journey itself does.
Also, it's nice to be able to check websites for prices of things you might need to check out. Greyhound tickets, train schedules, tickets. Where is the nearest liquor and when does it close? Oh, Google!
LastFM/Pandora and trivia apps are a great way to rock out and pass time when waiting for trains/hitching.
If you're like me and you love taking pictures and sharing them. This is exceedingly faster than shooting on film and waiting to develop them and possibly losing them. It's all a matter of preference, really.
Also, not to sound like a dick--but a smartphone isn't the best phone to let every kid without a phone use. There are people with sticky fingers, and smartphones are easy to hide and pawn.