One thing's consistent no matter your cell provider: it's hard to make calls when your phone's dead. Travelers who are constantly on the go and away from electrical outlets can try Novothink's Surge, a solar-powered charger that fits directly onto the back of Apple's iPhone. Leave it in direct sunlight for about two hours — say, on the dashboard of your car as you drive — and the Surge will give your phone enough of a charge to allow you to make a 30-minute call. It's not nearly as fast or reliable as plugging the phone into a socket, but when a socket's not around, it's nice to have the sun.