Starting with the iPhone 5, Apple has switched to using a single-chip LTE module which, by the way, costs $10 more than the cellular module in the iPhone 4s.
There has been talk lately of Apple possibly adopting a tightly integrated solution that would combine both LTE modem and a main processor on a single A8 chip, akin to many Android devices.
According to a new report by Fudzilla, this won't happen in the next iPhone generation as Apple is once again looking to turn to its longtime supplier Qualcomm for dedicated LTE chips...