How can I Ensure a Retired iPhone Stays Activated
I had the same "issue" with my iPhone 1. gen a few months ago. It was like four years ago I've been messing around with jailbreaks and what not. A buddy of mine asked if he could borrow my retro iPhone and there I was googling after an updated jailbreak.

Like you, I found a lot of forums with a lot of different solutions but I ended up with finding a download-link to a .ipsw which was already jailbroken/unlocked with the latest 3.1.3 version. Then I went to iTunes and restored the thing, and voila!

Of course I cannot find the exact .ipsw right now, but you cannot 'brick' the iPhone 2G, so you should be safe no matter what :)