How To Downgrade iOS 4 : iPhone 3GS

Downgrade 3GS to 3.1.2 on a Mac Downgrade 3GS to 3.1.2 on Windows 3.1.2 Firmware (Official Apple Links) Download iPhone OS 3.1.2 for iPhone 2G  Download iPhone OS 3.1.2 for iPhone 3G  Download iPhone OS 3.1.2 for iPhone 3GS 3.1.3 Firmware (Official Apple Links) - Only use these if you do not have 3.1.2 on file. Download iPhone 3.1.3 firmware for iPhone 2G  Download iPhone 3.1.3 firmware for iPhone 3G  Download iPhone 3.1.3 firmware for iPhone 3GS Utilities iReb for Windows (Mac Soon) iRecovery (Mac & windows)