Anyway, I would like to emphasize that this method only works and designed to deal with iPhone 4 baseband protection. Thus devices other than that, is not included. Therefore sorry.
Here are the steps you can follow to prevent iPhone 4 baseband update or protecting iPhone 4 baseband restoring to iOS 4.2.1.
- Download the newest version of TinyUmbrella.
- Also grab the latest greenpois0n rc5 update (http://greenpois0n.com)
- Launch TinyUmbrella
- Connect your iPhone then save SHSH (remember 4.2.1 SHSH were saved, don't continue if they were not saved)
- Launch TSS Server (If you get errors read the help section or FAQs or comment below typically it fails because you have some kind of web sharing enabled... use google to fix it - your issue really not much I can do...)
- Launch iTunes
- Choose your device name / type in iTunes
- Click Shift for Windows or Option for Mac restore -> Choose the 4.2.1 ipsw
- Restore SHOULD error with a 1013 error. Simply click "ok's", close iTunes.
- With your device sitting with the usb pointing to iTunes (recovery mode), enter DFU by pressing and holding HOME + POWER until your screen goes black... then after a count of 2 (1.5-2 seconds) let go of POWER but keep holding HOME. If all goes well you will see nothing but a black screen. If your timing is even a LITTLE bit off, you will see the apple logo and your phone will boot back into recovery mode... Go back to step 10 and try again.
- You're now in DFU mode. Start greenpois0n and press 'Jailbreak'
- Once greenpois0n has finished its thing. Press 'Complete!'
- Let your device restart. You should end up on the activation screen.
- Great, because the baseband was preserved and you are now on 4.2.1
- Put your device into DFU mode and then click 'Fix Recovery'
- Click 'Yes'
- Your device's screen will turn white and you will see debug boot information.
- Eventually your device will boot into the activation screen.
- Congrats. You're on 4.2.1 now :),
If the error 16xx occurs, you can put your device into DFU and then do the command on the step 5 above. And if you baseband was updated -- the restore doesn't end in a 1013 -- chances are because you had no the TSS server running or you didn't update with TinyUmbrella. Or the last possibility, your iPhone is not iPhone 4.Source; TinyUmbrella.