From ATT Customer Care Tweets a short while ago:
Question: "I want to preorder tonight for iPhone 6 from AT&T, but I also want to trade-in my old iPhone 4 for $200 toward phone. How do I do that?"
Answer: "You can get trade-in credit but the exact buy flow/page indicators for http://att.com still being determined. ^JasonS"
Seems they still have not quite figured out how they are going to do this.
Question: "I want to preorder tonight for iPhone 6 from AT&T, but I also want to trade-in my old iPhone 4 for $200 toward phone. How do I do that?"
Answer: "You can get trade-in credit but the exact buy flow/page indicators for http://att.com still being determined. ^JasonS"
Seems they still have not quite figured out how they are going to do this.