Google "apple understanding t mobile iPhone".
First hit for me shows which iPhone 5 is fully compatible with t mobiles 1700 band. Only sure way is to look at the last 4 serial numbers according to the apple support page.
I just took a look at the page. Very helpful. Thank you (x2)!
----------
It's a little more complicated with the 5. When the iPhone 5 launched in September 2012, it did not support all of T-Mobile's frequencies. When T-Mobile started offering the iPhone in April 2013, Apple revised the 5 to support T-Mobile's frequencies. But they didn't change the model number, so you can only tell by the serial number if you have one manufactured before or after April 2013.
Just read your post. Makes sense to me. Thanks for sharing.