I got a iphone 3gs 3.1.2 firmware new bootrom which was jailbroken by

[zamibd]

blackra1n How can I restore it to 3.1.2? I got a iphone 3gs 3.1.2 firmware baseband 05.11.07 new bootrom which was jailbroken by blackra1n about a month and half ago. is there any way to resore it to 3.1.2 i dont want it to upgrade it to3.1.3 . and if i had to upgrade is there any tools available to jailbrack 3.1.3 new bootrom. plz help