iH8Sn0w has successfully performed a tethered 4.0 jailbreak for iPhone 3GS devices with the new bootrom.
Unfortunately the jailbreak requires that you have your 3.1.2 SHSH blobs saved. Originally this was not planned for release; however, iH8Sn0w has agreed to make it public.
Alright... If anyone has their 3.1.2 SHSH blobs, NOT 3.1.3. Then I'll see if I can produce a tool that will do this job...
It could be available as early as tomorrow.
Below you can see a video demonstration posted by AKinGdom1...
