Jailbreak 3g?

[reesrk8]

This is prbably an easy question to answer, but I have searched but cannot find a definitive answer.
I have an iphone 3g, 3.1.3 with modem firmware 05.12.01
Can i jailbreak this current firmware?
if not, can i downgrade to 3.1.2 and then jailbreak?
i am not bothered with unlocking, only jailbreak.

thanks in advance,
Rog

 

[reesrk8]

Found it now, used redsn0w

 

[BENGRIMM]

You can also use Blackrain & its easier