I just called two local stores...the first store manager had no idea about the promotion and was trying to solve my question with information about their "normal" trade-in program. The second store I called tried to do the same, but I explained that AT&T just anounced today this new thing and all the carriers are doing it, etc...and she found an INTERNAL MEMO that explained minimum $200 for 4, 4s, 5, 5c and $300 for 5s. They have to be in good working condition she said, so nothing broken basically.
More importantly, she said "direct fullfillment" orders - aka online orders - are STILL ELIGIBLE for promotion. So stay up late and order at midnight! She explained that the memo said you can order online and pay the full price you would normally without the promotion, and then once you got your new iphone 6, you would trade in your old device in store and get an AT&T gift card. She said that I could use the gift card toward my bill, but I may have to buy an accessory in-store to do that?!?!
I'm very happy about this because I wanted to preorder at midnight to have it arrive on the 19th but still take advantage of the promotion!