Will T-Mobile's network be ready for the influx of new Apple subscribers? Remember that they have only been offering the iPhone since April 2013. Sprint and T-Mobile might steal a bunch of iPhone customers from AT&T and Verizon this fall.
AT&T currently has 39 million iPhone subscribers, compared with 31 million at Verizon, 14 million at Sprint and 4 million at T-Mobile.
http://www.fiercewireless.com/story/t-mobile-sprint-will-seek-feast-iphone-6-6-plus-release/2014-09-10