Good news for iPhone 4 users who were either running an older version of iOS for the jailbreak or running iOS 5.1 but were waiting for a proper untethered jailbreak.
iOS security researcher pod2g tweeted today that his iPhone 4 running iOS 5.1 is now running untethered. As of now, though, he may be the only one with the recipe to do this although we expect a redsn0w update to come out soon which will make it available for the masses.
As of now, it can only do a tethered jailbreak for the iPhone 4, meaning you will have to keep your phone switched on or you will lose it and have to do it all over again. Hopefully, the updated version is released soon.