^ yup thats what i did,
if you updated to the newest version 3.1.3
if its 2g and your model# starts with MC your fucked, if its anything else then you can download redsn0w (blackra1n won't work with 3.1.3)
use redsnow 0.9.4 and download the ispw/firmware 3.1.2 ( NOT 3.1.3) and it should jailbreak your 3.1.3