The way the Next trade in option works is you trade in your 7 after reaching your trade in point which means 12 payments on the 24 month plan or 24 payments on the 30 month plan. If you haven’t reached your trade in point, you need to make additional payments before you can trade in. The only credit you get for the trade in is the remaining Next payments you don’t have to make. You then start a new Next plan with the new phone. You might be better off just paying off the 7, get it unlocked and sell it yourself.
iPhone X – trade in options for iPhone 7?