I was Jailbroken under 3.1.2 then I reset and took it to an Apple Genius, however when they were working on my phone, they upgraded to the latest firmware (they told me it would fix my phone) so not knowing until they handed it back to me, now I have 3.1.3 
Be careful if you have to take your phone back to Apple and ask them not to install the new firmware. I told the guy I usually wait a couple of weeks to see what bugs may come out and it didn't matter to them at all.
Be careful if you have to take your phone back to Apple and ask them not to install the new firmware. I told the guy I usually wait a couple of weeks to see what bugs may come out and it didn't matter to them at all.