Placing order via AT&T's Website
I was able to place my order via AT&T's website (Apple's site was giving me trouble and timing-out). I have a family share plan with three lines. Two were eligible for the $199 early upgrade on a 16 GB iPhone 4. I added those with no problems.
I was also able to add a $499 32 GB iPhone to the third line. (This line didn't qualify for the full discounted upgrade pricing, as the upgrade date was 3 January 2011.)
I submitted the order right around 5:15 am EDT and received the email confirmation just a few moments later.
It's also worth noting that, for the two lines that were eligible for the early upgrades and the $199/$299 prices, the price showed up as $399 for the 16 GB model UNTIL I added it to the cart, at which point both were properly adjusted down to $199.
I hope this helps!