Jailbreak 3.1.x

[NiteQwill]

http://www.blackra1n.com/

Enjoy, works on two iPhones running 3.1.2.

If you want to keep your unlock, use Pwnagetool to upgrade from 3.0 or 3.0.1

 

[Tokiopop]

WHOA!?

Really? Are you serious? NO WAY.

https://forums.macrumors.com/threads/801112/

 

[dhlizard]

http://www.blackra1n.com/

Enjoy, works on two iPhones running 3.1.2.

If you want to keep your unlock, use Pwnagetool to upgrade from 3.0 or 3.0.1

Already a thread on this...

Blackra1n requires updating to official Apple 3.1.2 in order to use it so then your unlock is gone.