Contrary to the reviewer's comments about the Iphone 4's GPS in airplane mode being able to work...
According to http://support.apple.com/kb/ht1355
the GPS is disabled when in airplane mode. It is a complaint made by many, myself included. We want a wilderness-mode setting for the Iphone that turns off cellular network seeking, turns off wifi seeking, and enables gps reception. Apple ignores us, if enough complain perhaps we'll get it. Email email@example.com with a request for a wilderness-mode setting -- or a "enable GPS only" or something that will accomplish this.