I am sorting that out. Looking at the monthly upgrade program, the iPhone 7 128 is $35.68/mo. That's $856.32 over 24 months. Subtract $129 for AppleCare+ and that leaves a cost of 727.32. The outright purchase price is $749. It appears to be cheaper to do the installments on the upgrade program, if AppleCare+ is desirable. I suppose the catch is that it will be hard to NOT upgrade next year and return the phone and reset the payments for 24 months.
The base monthly plan without AppleCare+ and not part of the upgrade program comes out to $748.80 over 24 months for the same phone. Apparently the program is zero interest rate.