Apple continues to seek ways to counter the jailbreak, and the unlocking. With the arrival of IOS 4.2.1, the Cupertino company has introduced a new system requiring iPhone 4 users to update their baseband when they want to restore their device with
this firmware.TinyUmbrella, PwnageTool, or even Sn0wbreeze previously allowed to update your iPhone 4 with the last iOS n> not update your baseband. You can use Ultrasn0w to unlock your phone. But this is no longer possible with this new system, iTunes will tell you an error message, and you will remain stuck in recovery mode.
It is the site BigBoss who made the discovery of this little surprise in iOS 4.2.1:
It seems Apple has decided to audit the minimum necessary to baseband iOS. So for now, if you use the server or Saurik TinyUmbrella and try to restore 4.2.1 on an iPhone iOS 4, you will be in recovery mode and the software will not allow you to leave. In this case, you should either restore to 4.1, or 4.2.1 jailbreak with a tethered. Of course, if you need unlocked, I recommend you not upgrade to 4.2.1 iOS.
This is yet another reason for those of you who rely on a carrier unlock to STAY AWAY from Redsn0w and iOS 4.2.1.
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