After the release of PwnageTool 4.0, the users can actually jailbreak iPhone 3GS 3G iOS 4 with a stable and trusted tool from infamous iPhone Dev Team. Luckily, there is also no wait involved to unlock iOS 4 as ultrasn0w 0.93 does it for you. We might get sn0wbreeze 1.6 very soon. Both of these tools actually create custom firmware which does not upgrade your baseband.
If you are not interested in cooking these custom firmware [ipsw] and just want to restore it straight away for jailbreak, we have created these custom iOS 4 firmware [ipsw] for iPhone 3GS and 3G using PwnageTool 4.0/4.01. These custom firmware are different for unlockers [Unofficial Carriers] and official carrier users. Download the one according to your requirements and follow official PwnageTool 4.0 instructions.
The custom firmware are ready and links are being updated as soon as uploads complete. Stay tuned.
Update:All custom iOS 4 ipsw have been recooked using PwnageTool 4.01 and links are live except for 3GS official carrier which will be up soon also.
Download Custom iOS 4 Firmware for iPhone 3GS
3GS Custom iOS 4.0 Firmware [Unofficial Carrier IPSW (For Unlockers)] [iBooks Fix]
3GS Custom iOS 4.0 Firmware [Official Carrier IPSW] (iBooks Fix)
Download Custom iOS 4 Firmware for iPhone 3G
3G Custom iOS 4.0 Firmware [Unofficial Carrier IPSW](iBooks Fix)
3G Custom iOS 4.0 Firmware [Official Carrier IPSW] (iBooks Fix)
Unlock iPhone 3GS iOS 4 with ultrasn0w 0.93.
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