This post will help those who unlocked iOS 4.2.1/iOS 4.1 on their using ultrasn0w 1.2 and were experiencing GPS issues. The iPhone Dev Team have acknowledged the unfortunate fact of ultrasn0w causing loss of GPS for the iPhone unlockers.
The strange thing that comes out from their acknowledgement is that this loss of GPS is not a universal problem:
Unlockers have been reporting mixed results about GPS functionality at 06.15.00. Until we can track down what differentiates those who retain GPS vs. those who lose it, be conservative and assume you’ll lose GPS at 06.15.00. As we work on finding the cause (and possibly a fix), please report your personal findings in our comments section. (Update: early indications are that while 06.15.00 is capable of GPS, it will require some further hacks. But please still be conservative and assume you will lose GPS at 06.15, in case the hacks don’t work).
To sum it all up:
* By unlocking iPhone 3G/3GS with baseband 06.15.00, assume you will lose GPS.
* Baseband 06.15.00 does support GPS functionality.
* A few hacks are required to fix the the troublesome part
original link : kabatobato