How to downgrade from 3.0
So my brother and his company are a part of the developer program and I wanted to 'tag along' since I've started to learn how to develop (but I didn't want to pay $100

). I went ahead and upgraded to 3.0 because he said he would put my iphone on his list - well turns out he's not going to be able to do that... at least not now (but that's beside the point).
So last night I was stuck with an iphone (not part of the developer program) in 3.0, and I couldn't downgrade - I had a brick.
After a while of tinkering I've got the phone working again and running on 2.2.1!
To do this, I downloaded PwnageTool and created a custom .ipsw from 2.2 and it installed pretty well (however, it did take 2-3 tries for some reason...). Then, since I didn't want it jailbroken, I figured I would just update up to 2.2.1 and I would have a fresh legitimate updated firmware. iTunes erred again and now I'm starting the process over.
However, this time I made a custom .ipsw from 2.2.1. That went ok, and I had a working, jailbroken iPhone on 2.2.1 - again, though, I don't want it jailbroken (but if it's the only way for now, I'll keep it).
I just updated the carrier settings and I am currently restoring the phone to 2.2.1 - so that it will not be jailbroken.
--- Ugh ---
Well while typing that I got an error again from iTunes while I was attempting to restore from a jailbroken 2.2.1 to a fresh 2.2.1 - iTunes error 1013.
I am now going BACK to the jailbroken 2.2.1 since it atleast lets me use my phone. If I discover anything else, I'll post.
If anyone is able to fully bring it back to 2.2.1, please email me or PM me!