Regarding walk-ins: my sense is that no one at Apple knows the policy about walk-ins buying an iPhone. Most of the stores that I called stated that any shipments that they get, they are all for online reservations with instore pickup. Some stores stated that they do set aside a few from each new shipment for walk-in buyers, first come first served in the truest sense of the word. Some of those stores say different things different days. And some of the same employees, if I recognize their voice, have said different things on different days.
No one has accountability at Apple. They're still telling us that full price phones are locked. They are blatantly not.
Best course of action is to reserve online and then when you go to pickup in the morning, try to convert it to a device-only, full price sale. If they don't allow you to do that, then what are they going to do? They'll have an iphone in-hand for sale, and why shouldn't I be able to buy it outright. The chances of this succeeding are higher than lining up, in vain, outside an Apple store every morning.