I just picked up a 3GS yesterday off Craigs List. I looked on here and after getting some help from members (thanks again MexiChriS), decided I just needed to wait for an official 4.0 jb to be released. My 3GS is on 4.0 with no previous jailbreak history.

However, I read a post that described it might be possible to do with an older 3GS. I didn't realize this when I posted yesterday. This one has a model number (at least on the box) that starts with a MB and the 4th & 5th digit of the serial number is 25. If I'm still stuck, that's cool, but if there is a way to jb/unlock it, that would be awesome.

Thanks for any help in advance!