Can I upgrade iOS 3.1.3 without disturbing baseband 05.12.01?

[Little-Acorn]

My wife's iPhone 3GS 32GB, which I've mentioned on other threads here, has iOS 3.1.3 and baseband 05.12.01. That's very valuable to me - I can jailbreak it and unlock it WITHOUT installing the iPod baseband 06.15.00 which disables the GPS. In fact, I already have. It still has the 05.12.01 baseband, and the GPS works beautifully.

But now I want to install Navigon... and the Navigon website says I need at least iOS 4.something.

I know that if I do any upgrading of the iOS, I risk losing the jailbreak. Well, if I have to, I'll even do that... I can always jailbreak it again later.

But my question is, can I upgrade this iOS without disturbing the baseband it presently has (05.12.01)... and without winding up with iOS 5.1 which is un-jailbreakable? Is there a way I can wind up with iOS 4.2.1 or some similar thing? And the same baseband I have now?

 

[fijiman]

There is a jailbreak available for 5.1 but it's tethered...if you are lucky enough to own an "Old BootRom" 3GS iPhone you can jailbreak on 5.1 firmware Untethered...

You can update your iPhones firmware while preserving your baseband...either with a custom firmware with Sn0wbreeze or Redsn0w.....or using tools like TinyUmbrella Good Luck