As a new purchase? I'm guessing never, since the phone is over a year old, and there are some 7 Samsung smartphones that are now being carried that are newer.
If you're talking about a warranty or insurance replacement, those may come back into stock (particularly warranty replacements, which are refurbs).
Learn how connect your AT&T holiday gifts at Unwrapped on Wednesday, 12/27 (1-4pm ET)!
Is the iPhone X worth it? Find out why it totally is!
Find out how to track your iPhone's delivery!