YW. If anyone does get in a situation where they are out of cell coverage and using an iPhone for navigation, battery power management is something to keep in mind. Turning off items using Airplane mode is a great way to get just about everything powered down. Bluetooth and Wi-Fi can be turned on regardless so make sure they are also turned off unless you need them. With mine, going to Airplane mode turns them off, then I turn them back on separately if needed.

Apparently, turning location services on does not work the same way. As Chaos said, for the internal GPS to work, Airplane mode needs to be turned off (meaning phone stuff is turned on) and then individual items like cell coverage, wi-fi and bluetooth need to be turned off individually. Since you can't change batteries in an iPhone, managing the power you have is rather critical. $.02