Is there an app to disable everything but GPS on iPhone?

Solution 1:

If jailbroken, SBSettings allows one to turn off everything: Data, Wifi, Bluetooth, 3G, Edge, Phone, SSH, etc. but leave GPS enabled.

If not jailbroken, Settings > General > Network lets you turn off WiFi, 3G, BlueTooth, and Data, which leaves GPS, Edge, and Phone. Turn brightness all the way down. This ought to extend battery life quite a bit.

Solution 2:

I'd thought I'd share - the best way to do this without needing a paper clip and peeling off your case is to use the SIM PIN function. Turn it on (Settings->Phone-> SIM PIN) and reboot the phone. When it asks to unlock the SIM, just hit cancel. This will have the same effect as removing the SIM

Of course do to this you'll need the SIM PIN. For AT&T the default is 1111. You should be able to get your SIM PIN from your carrier.

Not sure if this works with non-SIM iPhones, i.e Verizon.

http://adventurealan.com/iphone4gps.htm