The Chronic Dev Team just released the corona untethered jailbreak for the iPhone 4S. On their blog, the Chronic Dev Team explains how hard it was to jailbreak the A5 processor.
You can download the Absinthe A5 Untethered Jailbreak for Mac right now, Windows and Linux versions are available later.
Now we just have to wait until someone releases a tweak for the iPhone 4S that reads the Siri keys directly from the iPhone 4S to make porting Siri to the iPhone 4 easier.