Hackers have released Sn0wBreeze 2.4 beta 1 utility, which is able to jailbreak the latest iOS 4.3.1. This jailbreak is tethered for
Sn0wbreeze also preserves your baseband, which is very useful for unlockers. Using Sn0wbreeze you can update firmware iOS 4.3.1, while preserve old unlockable baseband. It also works with iPhone 3GS with 06.15 baseband.
It is still beta, so there might be bugs so use at your own risk.
You can download Sn0wBreeze 2.4 beta 1 for Windows here.