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How To Downgrade iPhone 4 Baseband 4.12.01 to 4.11.08 On iOS 5.1

You can downgrade your iPhone 4 from baseband 4.12.01 to 4.11.08 if you accidentally updated your device to firmware 5.1 but this is possible as long as Apple is signing iOS 5.1. Downgrading your phone to BB 04.11.08 is important because hackers know much more about this modem firmware as compared to 04.12.01. Baseband 4.12.01 is quite new and chances of getting it unlocked within few weeks are quite low whereas 4.11.08 is in the limelight from many months and some hacker might come up with its unlock solution sooner or later.
downgrade iPhone 4

Important

  • Apple will stop signing iOS 5.1 soon, therefore, follow this guide as soon as possible.

Download

Tutorial To Downgrade iPhone 4

1. If you’re using iTunes 10.6 then uninstall it and use version 10.5 instead. The link is given in download section above. If iTunes gives error that you’ve new version already installed then you can bypass this error by searching for iTunes in search box present in “Start” Menu.

2. Rename the file “iTunes Library.itl”  to “iTunes Library.itd.backup” or the name of your liking. Run the setup again and the software will be downgraded to 10.5.

3. Now get iOS 5.0.1 for iPhone 4 from the download link we gave you earlier and put your device into DFU Mode. In order to get into DFU Mode you need to follow these steps.

  • Power off your phone.
  • Hold down both Power button and Home button for 10 seconds.
  • After 10 seconds, you need to release Power button but keep on holding Home button for another 10 seconds.
  • When you see black screen, it’ll mean that you’re now into DFU Mode.

4. Open iTunes and press “shift+restore button” in Windows or “alt+restore button” in Mac. Locate the stock iOS 5.0.1 file you downloaded earlier. iTunes will now restore your phone. After restoration process is complete you can use official SIM to activate your iPhone.

5. If you don’t have official SIM, then you can use custom firmware to activate it. Custom firmware can be created with Sn0wbreeze. In Sn0wbreeze, browse for iOS 5.0.1, hit next arrow, go to “Expert Mode” and select “Build IPSW” to create it. You can also use Redsn0w for this purpose.

6. Repeat the Step 3 and 4 again but this time point iTunes to custom iOS 5.0.1 instead of stock one. Congrats! You have downgraded iPhone 4 successfully.

Update: Apple has stopped signing firmware 5.0.1. This method wouldn’t work anymore.


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