Bad information is bad.
Originally Posted by Bloodkip
The Bootrom is what causes the new 3GS to be a tethered jailbreak.
The new 3GS with 3.1.3 is not unlockable or jailbreakable at this point in time. There is no native 3.1.3 jailbreak and I don't expect those that create the jailbreaks to work too hard on something with the iPad an 3.2 or 4.0 not too far off. You'll probably have to wait till March or June for a new jailbreak solution.
If you find a 3GS ( with the new or old bootrom ) with 3.1.2 on it, not 3.1.3, it IS jailbreakable, but you will likely have a tethered jailbreak (this is b/c of the new bootrom). Meaning you will have to re-run blackra1n every time you restart the phone. An inconvenience, but if you want a jailbreak it's what you have to do.