I have an iPhone 3GS, 32GB, Version 4.2.1, Modem Firmware 05.12.01. Got it on eBay last year, and took it to the local wireless pirate who jailbroke it and unlocked it. I've been using it on T-Mobile ever since, pretty successfully. I've also been using Garmin Navigator on it successfully, clearly the GPS chip is still working well. I ducked that bullet, did NOT install modem 6.15.00. I had access to T-Mobile, had a GPS that was working great, all was well. Fast forward to August 2013. Now I'd like to load the latest version of the Geocaching app... but it says it requires iOS 5.0 or later. I'm worried that I might mess up the jailbreak/unlock if I upgrade the iOS on this phone. As I recall, my present iOS (4.2.1) is one of the few that this jailbreak/unlock can work on... or it was last year, anyway, when I had it done. A year has gone by since then. Now, is there any way I can upgrade to iOS 5.0 or later, without messing up my jailbreak? Or, any way that AT&T can unlock this phone "for real", so I can upgrade without fear, still use it on T-Mobile, and still have an operating GPS?