I have an unlocked iPhone 2G running the 3.0 OS. I don't have a Mac, so I can't upgrade my phone to 3.12 with pwnage. But I was wondering, if I upgrade my phone to 3.12 factory, will that re-lock the phone, or does it only undo the jailbreak part?
I'm not entirely sure how exactly 2G phones work, but I'm fairly certain that upgrading to 3.1.2 factory will re-lock and un-jailbreak your phone. However, you can re-unlock it using pwnage tool (or finding a custom IPSW on a bittorrent tracker - I just looked but there was surprisingly little. You'd be looking for something like iPhone Custom Restore 3.1.2 iPhone 1,1).
^Correct U should not just restore to 3.1.2 via itunes go ahead and create an custom ipsw 3.1.2 then shift+restore to it via itunes. Create this custom ipsw from pwnage tool or google and find a custom one and restore to that on your Windows pc.