Well, you still don’t get the promised ultrasn0w tool yet but the iPhone Dev team has gone ahead and released redsn0w that jailbreaks all the iPhone and iPod Touch devices except iPhone 3G S and even unlocks the first-gen iPhone. The jailbreaking tool is available for Mac OS X via Pwnage Tool and Quickpwn, which in fact also works for Windows.
The latest redsn0w tool however, comes with some strings attached like iPhone 3G users with yellowsn0w unlock should not use it until they release the ultrasn0w that contains the unlocked baseband. Also, as iterated before, the redsn0w will not work with iPhone 3G S, which hints that a special iPhone 3G S ultrasn0w might be under construction.
You can read more instructions, get the official and mirrored download links from over here.