We already mentioned in our 3.1.2 Firmware Jailbreak post that blackra1n is a software which can only jailbreak iPhone 2G,3G,3GS and iPod Touch, it can't be used for unlocking. Dev-Team has also released an official statement regarding this stating:
Contact Us for News Tips, Corrections and Feedback
Update: Geohot released a Windows jailbreak called “blackra1n” which is similar to redsn0w in that it covers multiple devices (and it covers beyond just firmware 3.0.1 where redsn0w currently stops). blackra1n is not a carrier unlock. You must always avoid updating your baseband to maintain your unlockability. If you use blackra1n to jailbreak 3.1 or 3.1.2, the steps you take before running blackra1n will prevent the unlock from working on your iPhone for potentially a very long time.