I was in a similar situation. I was in Canada and didn't want to Roam Internationally. So, I put my phone in Flight Mode. The GPS would not work at all in FLight Mode. I was using Garmin-XT. I tried every regedit that was posted and nothing. As soon as I turned off Flight Mode, it would get a lock. I wasn't using the data connection or the phone.... but Flight mode turned off the radio which would then turn off the GPS. I even posted this a while ago on
http://forum.ppcgeeks.com/showthread.php?t=31539