It looks like Apple has just added another hurdle for users who want to unlock their iPhone.
It seems that Apple has decided to put a baseband requirement on iOS. So at this point, if you are using Saurik’s server or tiny umbrella and trying to restore 4.2.1 on an iPhone 4, you will end up in recovery mode and tiny umbrella will not be able to pull you out of recovery.
This means that tools like Firmware Umbrella allow you to update your iPhone 4 to the latest firmware but preserves the baseband from getting upgraded will not work.
Semaphore has provided the following advice if you are stuck while trying to restore iOS 4.2.1 on an iPhone 4:
In this case, you will have to restore 4.1 again or you will have to restore 4.2.1 stock and be tether jailbroken. (Of course, I recommend 4.1 and not bothering with 4.2.1 at all). If you are an unlocker, this is a no brainer. Do not update to 4.2.1 even to test it at this point.
However, MuscleNerd has clarified that this change seems to only impact Firmware Umbrella:
4.2.1 is running fine on my i4 with 01.59 BB. I think they simply killed Umbrella way.
If you want to software unlock your iPhone then you should stay away from iOS 4.2.1 and also avoid tools like Redsn0w.
Apple continues to up the ante in the cat and mouse game with the iPhone hacking community. Let us know what you think in the comments section below.
[via Firmware Umbrella blog]