iOS 4.2 which has already been jailbroken on older iPhone's with the pwnage tool for Mac but now it has been confirmed that its also coming on the Windows which is some great news for PC users and that too with Sn0wbreeze.
The dev iH8sn0w of the Sn0wbreeze revealed that the iOS 4.2 has been jailbreaked on iPhone 3GS but he also mentioned that jailbreak App Stores Cydia, Icy and Rock (which recently merged with Cydia) were not really working for now. But dont worry because he said that they are working on it and they will work soon.
There was also a video revealed by DinoD7 which shows a iPhone 3GS (old bootrom) jailbroken with Sn0wbreeze. You can view it below.