when you buy an iPhone, and picking a carrier.not only does it come with that carrier's sim card, but it is put in a book of imei numbers that belong to that carrier. in order to activate a sim card for a new line of service, the iPhone must be in their book. if it is not in their book of iPhones they will not sell you service.
the iPhone 6 was sold for " AT&T / Verizon and T-mobile " and "AT&T Verizon T-mobile and sprint" if you bought the unlocked version like i did on launch day, you had to wait about 60 days for the imei number to be added to the phone companies book. Verizon took 1 year before they white listed all unlocked iPhone 6 and 6+ phones on august of 2015, prior to this date the phone worked on verizon, but only if you used a pulled pre-activated sim card from another phone.
here is an old post
https://www.reddit.com/r/verizon/comments/3gw0kw/psa_verizon_just_whitelisted_the_iphone_6_and_6/?
the 6s and 6s+ is being sold now as "Verizon Sprint T-Mobile " and " AT&T " , the AT&T has 1 extra band. AT&T will not sell you a sim card online if you have the wrong model. they treat it like a black listed phone. i know this because i had a blacklisted amazon fire phone that i got from eBay, and i hit the same wall when i called them on the error i was receiving.
when i purchased my 6s+ , sprint told me my iPhone was not one of their devices, despite it being one, on september 27 2015. i had to wait until November 17 2015 , for it to be listed as compatible
on the same day september 27 2015, Verizon also told me my iPhone would not work, and they could not guarantee it.
for a while there, i wanted to return it for the sim free version, but i couldn't get one in stock by the return date on the receipt
from my experience if you buy the unlocked phone ( T-Mobile ) , it will eventually be white listed. ( with the exception of iPhone 6 on sprint they continue to want bands 38,39,40,41 or whatever )
if you buy the "sim free one" then i think it is white listed out of the box
this year apple changed the LTE page and now says "sim free" contains all the bands and carriers from the other phone
it looks to me when iPhones are sold , there is a 70 day waiting period for " carrier exclusivity " where the phone carriers refuse to activate each other's handsets
the only real difference between ' unlocked ' and ' sim free ' is the imei device list that the carriers have.
[doublepost=1460562493][/doublepost]it was about 90 days between ' unlocked ' and ' sim free ' on the 6
[doublepost=1460563110][/doublepost]looking at the iPhone lte page. if you buy A1662 and unlock it . sprint will probably not sell you service.