UPDATE: This method WILL work for iPhone 4 RESTORING to 4.3
This page ONLY deals with iPhone 4 baseband protection. I’m sorry this will not work for any other device.
You can protect your iPhone 4 BB restoring to iOS 4.2.1. Follow these steps exactly:
Get the latest TinyUmbrella.
Get the latest greenpois0n rc5 update (http://greenpois0n.com)
Plug in your device and save SHSH (make sure 4.2.1 SHSH were saved, if not don’t bother continuing)
Start 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…)
Select your device in iTunes
Shift(windows) / Option(Mac) restore -> Select the 4.2.1 ipsw
Restore SHOULD error with a 1013 error. Click the “ok’s” and 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.
Congrats your baseband was preserved and you are now on 4.2.1
Put your device into DFU mode and then click ‘Fix Recovery’
Your device’s screen will turn white and you’ll see debug boot information.
Eventually your device will boot into the activation screen.
Congrats. You’re on 4.2.1 (again)? :)
If you get a 16XX error then try entering DFU and go to step 5.
If your restore does NOT end in a 1013, it means your baseband was updated. This is likely because you did not have the TSS server running OR you updated without TinyUmbrella OR you are working with a device OTHER than iPhone 4.