Jailbreak iPhone 3GS/3G iOS 4.2.1 and Update to Baseband 06.15.00 with RedSn0w 0.9.6b5 – iPhoneHeat

It is most likely the baseband, yes, rather than ultrasn0w. The GPS unit seems to be tied to the SIM card via the baseband somehow, since if you remove the SIM on a normal iPhone, the GPS chip stops working in much the same way as the new 6.15 baseband ..

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