I've got a 3G that is currently running iOS 3.0.1. I would like to jailbreak it, so I don't want to run 4.x. But I would like to something higher than what I"m on right now (like 3.1.3). Is there somewhere I can download the OS, and how do I install it? iTunes only offers the latest OS version. Can I download it (where?) and do a restore? I'm planning on jailbreaking.