Hacker I0nic has given his untether exploit for the iOS 4.3.1 jailbreak to the iPhone Dev-Team. They will perform testing and integrate it into their jailbreak utilities - redsn0w and pwnagetool. This untethered jailbreak will probably work for iPhone 3GS, iPhone 4, iPod Touch 3G, iPod Touch 4G and iPad.
The iphone-dev-team is already beta-testing the untether. So it is up to them to give you your tool of choice.
Please don't bother the dev-team now. The deal is: if the beta test is successfull, they are free to do whatever they want with it.