Preserve Baseband with Custom iOS 5.1.1 for iPhone 4 or 3GS with Redsn0w 0.9.11b4

The latest version of redsn0w now supports building custom iOS 5.1.1 firmware to preserve your baseband. Here’s how to build your own custom iOS 5.1.1 firmware.

UPDATE: Click here to factory unlock AT&T iPhone or other networks.

Let’s get straight to business:

1. Download the latest version of redsn0w from Dev Team’s blog.

2. Download original iOS 5.1.1 IPSW for iPhone 4 (GSM) or iPhone 3GS directly from Apple.

3. Launch redsn0w and go to Extras > Custom IPSW.

4. Point to the IPSW you just downloaded in Step 2. If you have a 3GS, you will be prompted whether you have a 3GS with old or new bootrom. Select appropriately.

5. Redsn0w will start building custom iOS 5.1.1 while disposing the files that will update your baseband. Once completed, you will find this file on the same file path as the original IPSW with the prefix “NO_BB…” followed by the file name.

6. Be sure to pawn DFU your iPhone with redsn0w by going to Extras > Pwned DFU. Simply follow the on-screen instructions.

7. Once your iPhone is in DFU, launch iTunes and press Shift+Restore (Windows) or Option+Restore (Mac). Be careful not to select the wrong IPSW during restore! If you get error 3194, you need to edit your hosts file. See here.

8. Wait for it to finish. Your iPhone will attempt to reboot and may stuck on the Apple logo with empty progress bar due to tethered jailbreak.

9. Launch redsn0w again > Extras > Just Boot. Follow on screen instructions.

10 .Your iPhone will boot up normally and follow the instructions here to unlock with ultrasn0w.

That’s it! If you encounter any issue, leave your comments below.

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