Jailbreak iPhone 4 on iOS 4.2.1 GM Using Redsn0w [Guide]

Yesterday Apple released iOS 4.2.1 GM for all idevices including iPad and iPhone 4 to fix the Exchange and Voice related issues. Fortunately iOS 4.2.1 is jailbreakable with Redsn0w 0.9.2 b2 on iPhone 4.

Redsn0w doesn’t support the iPad because Redsnow 0.9.6 b2 version, which we are using in this guide, was released to jailbreak upto iOS  4.1 and as you know iOS 4.1 is compatible with iPhone and iPod models, that’s why Redsnow can’t jailbreak iPad on iOS 4.2.1.

Follow these simple steps to jailbreak iPhone 4 running on iOS 4.2.1 GM. Unlockers and those who don’t know how to install jailbreak-apps via SSH should keep themselves away from all this stuff because there is no unlock available for iOS 4.2.1 yet and Cydia app is still broken on this version of iOS.

If you have already updated your idevice to iOS 4.2.1 and now want to downgrade it to previous versions like iOS 4.1, 4.0.1, 4.0.2, head over to this post for more details.

Step 1: Download iOS 4.2.1 GM (links to downloads or download pages are listed at the bottom of this post).

Step 2: Download iOS 4.1 final version.

Step 3: Download Redsnow 0.9.6 b2.

Step 4: Using the iTunes 10.1, update/restore your phone to iOS 4.2.1 GM downloaded in step 1.

Step 5: Start the Redsnow jailbreak tool and open the iOS 4.1 in it to star the jailbreak process. (Please make it sure that you selected the iOS 4.1 IPSW file in this step).

Step 6: Press the Next button after Redsnow identifies the IPSW file successfully.

Step 7: Now check the Install Cydia Option. You can also select any other option if available.

Step 8: Switch off your phone and connect it with the PC before you proceed.

Step 9: Follow the Redsnow on-screen instructions to put the iPhone into DFU mode.

Step 10: Wait a few seconds for redsn0w to do its thing. After you receive the DONE message, close Redsn0w and enjoy jailbroken iPhone on iOS 4.2.1.

Downloads:

• Download iOS 4.2.1 GM Release
• Download iTunes 10.1
• Download Redsn0w 0.9.6 b2
• Download iOS 4.1 for iPhone 4

Note: If you rely on unlock, don’t update you device to iOS 4.2.1 otherwise you’ll losecarrier unlock and there is no unlock available for iOS 4.1 and above yet.

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