@stephenP "I'd like to be able to use GPS without having my phone chew up a ton of battery life trying to find a cell signal.
I know the phone was designed to use cell towers and wifi along with GPS to find your location, but it has worked fine for me with just GPS.
Currently, you can shut off wifi and close down apps to save battery, but putting the phone in airplane mode will disable GPs as well. With the AT&T phones, you used to be able to remove the SIM card to disable the cellular antenna. Not sure if it still works that way."
If you turn on the SIM PIN on iPhone with AT&T contract, you can disable the phone's attempts to connect with cellular network in backcountry (saving the battery) and still use GPS and everything else. This works with iPhone 4, 4S, and 5. The default PIN that the iPhone 5 ships with is 1111. Not sure about 4 or 4S. In Settings, go to Phone, scroll to bottom, turn SIM PIN on, and change it to whatever number you like better than 1111 or leave it alone. When you turn the phone all the way off, then on, it will ask you to either enter the SIM PIN or not. Do this again to re-enable the SIM if you want to make a call, text, or access internet. You can still use the a wifi connection (if available) even with SIM turned off.