I've tried using the iPhone app Trails while up in the sky (with the usual little to no reception you tend to get) to track my flights and gone so far as to putting the phone beneath the windscreen to give it a good line of sight to the sky. It doesn't seem to work too well at all, I'm not too sure if that's a hardware or software issue though. That's all I can report on at least, however there do seem to be aviation related navigation apps available for the iPhone and iPad.