The problem with a smartphone app is battery life and recharging the phone. Many phones do not have replaceable batteries. My GPSr uses 2 AA batteries that can be easily replaced. I carry spares. In contrast, my Blackberry has a short battery life and although I could, I don't own a spare battery for it. Phones like the new Motorola Razr do not have replaceable batteries. If you carry a phone for emergencies, then kill the battery using it as a GPS with no way to recharge it, you've defeated the purpose of having it with you. I wouldn't carry a phone unless I had a solar panel to recharge it. Better yet, a SPOT, PLB or sat phone for phone or emergency use.