Restore iPhone 3GS, 3G to iOS 4.2.1 / 4.1 on 06.15.00 Baseband After Using Ultrasn0w 1.2 [How to Guide]

In case you have unlocked your iPhone 3GS / 3G by flashing iPad baseband 6.15.00 with ultrasn0w 1.2 on iOS 4.2.1, and have issues while restoring your device, here is Sherif Hashim the guy behind ultrasn0w unlock tool, has posted a simple guide showing how to restore your iPhone 3GS / 3G to avoid iTunes errors.

Note: To restore your iPhone 3GS from 4.2.1 to 4.1, you must have saved SHSH blobs for iOS 4.1.

For PwnageTool users:

A :  If you are on Mac and use PwnageTool: If you used pwnage tool then you will have to create a �new� custom 4.1 or 4.2.1 and say �No� when you are offered the BB update to 6.15.00 since you already have it, then build the custom ipsw and restore to that.

For Redsn0w users:

B : If you use(d) Redsn0w:

B.1: If you are currently on 4.1, then you can restore to official 4.1 again, and when you see error 1015 pop-up, you kick your device out of recovery mode using TinyUmbrella, use redsn0w and don�t check �ipad BB update� because you already have that Here Is How To Restore iPhone 3G And iPhone 3GS While On Baseband 06.15.00 And Having Issues icon smile

B.2: If you are currently on 4.2.1 then you�ll have to restore back to 4.1 (because 4.2.1 will not allow you to kick the phone out of recovery when 1015 occurs due to the silly BB / iOS mismatch check added there) , then do the same steps as CASE-1.

How to go again to iOS 4.2.1:

If you want to go again to 4.2.1 your only way is to use a custom 4.2.1 done by pwnage tool in the same steps mentioned in A .

Try Hashim's methods above to restore you device between 4.2.1 and 4.1, it worth trying. Don't forget to tell us about your experience.