If I preorder the iPhone 8 on att next, will I be able to trade in my iPhone 6s and then use those funds as a down payment when I pickup the phone at an Apple Store on 9/22?
You cans sell your 6s ahead of time and have the cash in your bank funds. Then at the time of checkout for your new 8, you can put a downpayment and that will reduce your monthly payments as long as you're on NEXT.