[ame=http://www.youtube.com/watch?v=ZlewvG56t3I]YouTube - Blacksn0w ported to 4.0 in action on a 3GS 4.0 beta 4[/ame]
It's impressive the amount of work that is being done with iPhone OS 4.0 Beta inside the Jailbreaking community. Not only do we have jailbreak tools for iPhone OS 4.0 Beta, but now we have the ability to unlock 4.0 on the iPhone 3GS. While these tools and the beta are not practical at this moment, it's great news for developers that are stuck with the beta and need to be unlocked.
Msft.guy has released a video demonstrating the unlock and how he has managed to port Blacksn0w to be compatible with the new beta operating system. He also provide instructions on how to do this yourself. The video itself is only a proof of concept, and here's why. There are still some bugs involved so it will be a pain in the *** to stay unlocked. Each time you reboot your device, you will need to re-apply the patched files.
A word of caution as usual; if you are not a developer, you shouldn't be playing with iPhone OS 4.0. IF you have a good reason to be using this, you will need to be on baseband 05.11.07 in order for this to work. If you don't know what your doing, stay away from this.
We strongly suggest you stay away from playing with any unlocking tools until the iPhone Dev-Team released their unlock for 3.1.3, which isn't far away, as the new 4.0 should be available shortly after WWDC.