iOS beta 6.1 4 was released this evening by Apple, and the new version of the operating system can be jailbroken using redsn0w 0.9.15 beta 3. Following this tutorial, exactly as it is explained, you can do it jailbreak for iPhone 3GS and iPhone 4 on iOS 6.1 beta 4, but you must be careful to follow the tutorial closely. Unfortunately, you may encounter problems using Cydia on this version of iOS, so do not jailbreak unless you are willing to restore again.
