Redsn0w 0.8 is a tool to jailbreak iPhone 3GS (OS 3.0 firmware). Redsn0w 0.8 enables many different add-ons and themes that was not possible with earlier versions of Redsn0w. Redsn0w 0.8 is available for download for Windows, Mac as well as Linux support too. All the updates to ultrasn0w, MobileSubstrate, and WinterBoard are all handled directly through Cydia (after you’ve jailbroken!)
After jailbreaking your iPhone 3GS, Unlock Your iPhone 3GS OS 3.0 With UltraSn0w. Ultrasn0w is also updated to 0.8 to unlock iPhone 3GS. After unlocking with Ultrasn0w on 3GS just reset your network settings (Settings->General->Reset->Reset Network settings).
Download Redsn0w 0.8 to Jailbreak iPhone 3GS 3.0
Use This link http://www.gadgetsdna.com/jailbreak-ios-4.3.2-using-redsn0w-0.9.6-windows-mac-guide/10567/