Forgive my ignorance because I am new to iPhones.
What about the info posted here
http://www.apple.com/iphone/LTE/? It shows two different models:
1. A1633 which lists At&t and Cricket and
2. A1638 which lists Sprint, Tmobile, and Verizon.
I'm a prepaid Cricket (at&t subsidy) and I purchased the contract free T-mobile phone because I assumed it was unlocked and i could pop my cricket sim in and it would work. A rep told me I would have to activate it with one of the four major carriers first. This made no sense to me since there are two different models and neither one of them support all four networks.