UPDATE: 10.20.2018 “With more than half of all iPhone buyers opting for installment plans”
The latter half of September, summer into fall for those of us north of the equator, has become a Groundhog Day  of sorts for me. A new iPhone is announced. I place an order and survey the market for my now nearly one year old model.
I begin with the eBay app, continue to Craigslist, then review commercial offers, from firms such as Gazelle and more recently the Apple Store app, conveniently displaying an estimated value during the purchase process.
For me, Gazelle and Apple’s offer represent the “bottom” of the market. eBay seems to reliably display a few euphorically priced examples, providing the top.
So equipped, I proceed. I’ve done the range over the years with mostly good results.
This year, I posted photos on Craigslist at a middling price. I received 6 offers (and one obvious scam) within 60 minutes and made arrangements to meet the successful bidder at a local coffee and tea establishment.
The buyer added his SIM card to my unlocked iPhone X, then connected to the internet via the coffee house’s wifi service. He passed the cash to me and handed the iPhone to his mother, bound for Delhi in the morning.
I later learned that they had been acquiring inventory for much of the day. “People in India love iPhones, but they are very expensive”.
Fittingly, this experience provided an answer to my question on secondary market iPhone value in light of Apple’s efforts to push new model prices up .
While contemplating the market, I wondered how the following facts might affect future cash buyer demand?
A. Cellular network operators (an oligopoly in the United States) have a bottomless pit of financing and contractual lock-in techniques. How many Americans understand the concept of an “unlocked iPhone”?
B. Apple is promoting an iPhone Upgrade program, with monthly payments “beginning at $37.41“. A recent Apple Store visit revealed a table full of iPhones displaying monthly payments on their screens. 
C. Apple is getting into the used hardware purchase and remarketing game, joining many auto manufacturers’ “Certified Pre-Owned”  experience. “There is nothing new under the sun” – Ecclesiastes 1:9.
D. Cellular operators are bundling services in an effort to to maintain, if not grow revenues. 
E. A meaningful introduction of the e-sim  offers both Apple and the cellular operators, fueled by Apple Pay (Apple’s own “currency” – why not?) new price, experience and contractual spaghetti opportunities. 
I sense that it will become more difficult to simply purchase an iPhone, unlocked. Perhaps Apple will use future price signals to help us do the right thing and pay monthly..
Apple Pay awaits our glance.
 Groundhog Day.
 A Dediu chart
 iPhone Upgrade Program
 T-Mobile offers a Netflix bundle while Verizon is promoting a “free” six month Apple Music subscription.
 Apple e-sim. AT&T, T-Mobile and Verizon support Apple’s e-sim. Presumably the required deal making software has been completed.
P.S. Jean-Louis Gassee has used the term “cashectomy“, occasionally while discussing cellular operators. I seem to recall that Mr. Gassee applied the term to the early Apple + Cingular (AT&T) relationship that launched iPhone v1.
P.S. You Probably Bought Your iPhone With This Bank’s Help. Its Stock Is Worth Buying, Too by Lawrence Strauss: