Unlocking iPhone 3GS? (New bootrom, 3.1.3, BB 05.12.01)

[Hmar9333]

Guys is it possible to unlock an iPhone 3GS running 3.1.3 on the 5.12.01 baseband?

It's an MC model (new bootrom), but the Ultrasn0w page on cydia doesn't specify if I need to be running 4.0 or not.

[worldcup1100]

Guys is it possible to unlock an iPhone 3GS running 3.1.3 on the 5.12.01 baseband?

It's an MC model (new bootrom), but the Ultrasn0w page on cydia doesn't specify if I need to be running 4.0 or not.

From the Dev Team blog:
Baseband Unlock

As you probably know by now, ultrasn0w has been updated to cover all basebands from 04.26.08 onward. Many thanks to @sherif_hashim for finding the crashing command that the new ultrasn0w 0.93 uses! He worked hard at finding the crash, and he kept it confidential until the right time to use it.
Major props to @oranav (who found the earlier +xlog crash). He also had this crashing command!
iPhone 3G and 3GS baseband unlockers (those who rely on ultrasn0w to make phone calls) should always be very wary to update their firmware, however our Ultrasn0w application will unlock all recent (including the current) 3GS and 3G baseband firmware versions. Once you are jailbroken using PwnageTool 4.01, install ultrasn0w from Cydia and you’ll be unlocked.
Remember! This baseband unlock situation is rare, should you upgrade your iPhone blindly at the next iOS release please don’t expect an unlock - but for now you are OK (whatever state your baseband is in).

So, yeah you can unlock. You wouldn't be able to on 4.0, but on 3.1.3 yes you can.