If you have updated your iPhone 3G(S) baseband to iPad baseband 06.15.00 in order to unlock it on iOS 4.2.1 and now you are having issues while restoring the device, Sherif Hashif has posted a simple method which we are going to share with you people.
In case you want to restore iPhone 3GS back to iOS 4.1, you must have saved SHSH blobs for 4.1 IPSW.
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.
B. If you use(d) Redsn0w:
Case 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
Case 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.
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 .
It is to remind you that iPhone Dev Team is also working on a new hack which will also allow users to downgrade the baseband from 06.15.00 to any previous baseband like 05.15.00.
- iPhone Dev Team Working on Downgrade for iOS 4.2.1 on iPhone 3GS and 3G (crenk.com)
- iPhone 4 Baseband 2.10.04 Unlock is possible (geniusgeeks.com)
- [How to] Update iPhone 3GS/3G Baseband to 06.15.00 with PwnageTool 4.1.3 (geniusgeeks.com)
- Redsn0w 0.9.6beta5 For iOS 4.2.1 Released To Unlock iPhone 3GS & iPhone 3G (iphonehacks.com)
- Upgrade iPhone 3G, 3GS Baseband 06.15.00 with PwnageTool Unlock Edition (ihackintosh.com)
- Download Ultrasn0w 1.2 to Unlock iOS 4.2.1 on iPhone 3GS/3G [Updated] (geniusgeeks.com)
- PwnageTool 4.1.3 Unlock Edition to Update iPhone 3G/3GS Baseband (crenk.com)
- Unlocking iPhone After Updating Baseband To 06.15.00 Causing GPS Issues? (iphonehacks.com)
- Download Redsn0w 0.9.6b5 to Update to Baseband 06.15.00 on iPhone 3GS/3G running on iOS 4.2.1/4.1 (geniusgeeks.com)
- iOS 4.2.1 Unlock Released With PwnageTool 4.1.3 for iPhone 3G/3GS (techie-buzz.com)