Why not use the iPhone Upgrade Program? As I understand the iPhone Upgrade Program:


A 64GB iPhone 6S bought upfront costs $749, and AppleCare+ costs $129, for a total of $878.
A 64GB iPhone 6S bought on the iPhone Upgrade Program (which includes AppleCare+) is $36.58/month for 24 months ($877.92), but you can trade in your iPhone for a new iPhone after 12 months (having paid only $438.96) if you commit to another 24 months of payment for the new iPhone.


Aren't you effectively only paying half price for every iPhone you get under the iPhone Upgrade Program until you decide to get your last iPhone ever? This sounds too good to be true. Is there any downside to this?
The "downside" is that you lose the hardware. That's Apple's entire incentive for offering this exchange feature. If you're ok with the reality that you must exchange the phone you "half-own" in order to receive a new model early, there is nothing further that should stop you.