Downgrade iPhone 3GS to iOS 4.1 without shsh blobs.
1. Download the iPhone 3GS firmware.
2. Start RedSn0w 0.9.15b3 as administrator in Windows 7.
3. Click on Extras and SHSH blobs.
4. Click New and select the firmware file for iPhone 3GS. Redsnow will process, but return with and errormessage. Ignore that and go to Pwned DFU. Put the iPhone in DFU mode and run Pwned DFU.
5. Close RedSn0w and start iTunes. When asked to restore the iPhone hold down the shift key and select the firmwarefile for iOS 4.1 to restore. The iPhone Restores but iTune will return an errormessage because of missing baseband. and the iPhone show the restore picture.
6. Close iTunes and open RedSn0w as administrator and select Recovery Fix. Put the iPhone in DFU mode and recovery
fix will run. This action will download the missing baseband and set the iphone in welcome mode.
7. Close Redsn0w and open iTunes.
8. Activate the iPhone with iTunes. Now the iPhone runs non Jaibreaked iOS 4.1
9. Save your SHSH blobs with a shsh blobs saving tools in case Apple stop signing iOS 4.1
10. You can jailbreak your iPhone by open RedSn0w as administrator and select Jailbreak.