Pre-order iPhone with trade-in?

With past pre-orders, you've needed to pay at time of pre-ordering.

Since nothing has been said of any new iPhone or how the pre-orders will work if one is to be released, no way to know if that will continue to be the case.

You can submit your device for a trade up, and get a gift card by email, and use the gift card at the moment you pre-order it.

Read here for more details on the Trade-Up program.

iPhone Trade-up - Apple

With that said, you are very likely to get more for your current iPhone if you sell it privately than what Apple may give you.

You cannot get credit for the old phone until it can be physically inspected at an Apple store, or sent in to BrightStar, Apple’s recycling partner. Only after direct physical inspection is the final trade-in value determined and the money/credit given to you.

All you get before that is an estimated value, but no actual money or store credit.

Any order from the Apple online store requires payment in full at the time of ordering. A hold for the amount is placed on your credit card, and then actually charged when the item(s) ship. Any Apple store credit you want to apply to the charges needs to be applied at the time of ordering.