I have already made all 12 of my payments and AT&T told me that there would be an "upgrade fee" equal to one month's installment if I wanted to preorder at midnight. I decided to just pay the rest of it off and sell my phone because I will come out better financially. Also, I was told (if I went the first route) that I could preorder through either Apple or AT&T.
As for the Apple plan or AT&T Next, I'm also curious to find out.