I want to take my 3G hiking and use it for GPS. I can download a map so all I'll need is to get a GPS signal. Saving battery life will be important so I wondered if I can turn off the phone function. Airplane mode won't work as it would block the GPS. I tried using the SBSettings for the phone but I get a "Dependency" alert in Cydia (for 4.2.1) and can't install it. And closing the Phone process doesn't seem to work either. The phone just comes back on. Is there another way to turn off the phone? If I don't have a signal would it still be draining the device looking for a signal?