Well you can't have an unlock without a jailbreak.
Originally Posted by blablagirl
That's probably because you are looking at blackra1n which strictly jailbreaks.
The Dev Team just released PwnageTool 3.1.4 that will jailbreak the newest firmware, but as of now, 3.1.x firmware is not unlockable from what I've read. You can jailbreak it, but not unlock.
If you download the 3.0 ipsw and manually upgrade to that, you should be able to jailbreak and unlock again, just do not install 3.1.x versions - as you will lose your unlock and not be able to get it back.
There are several threads already about manually installing a firmware bundle, so I'd start there.