Lenovorola disabled Band 12 support on
all 2015 (3rd gen) Moto E/G/X phones that initially had it, except for the Moto X Pure Edition. On the MPXE they bungled VoLTE support such that users of certain networks, most notably T-Mobile's, experience call breakup that is sometimes so bad a call cannot be maintained. Lenovorola's work-around for the problem is to disable VoLTE. According to users who've called: Their CSRs have stated Lenovorola has no plans to address the issue until (and unless?) they release Android Nougat for the MXPE, which may (or may not) happen sometime this fall. Another user who called claimed a Lenovorola CSR told him they've had few complaints about the problem, the implication being they don't regard it as particularly pressing.
Here's the thread on Lenovorola's site:
Choppy call audio after MM upgrade w/VoLTE
FWIW: I have a colleague at work with an MXPE on TMO. He's experienced the problem. His next phone won't be a Lenovorola device.
Nor, it's increasingly likely, will be mine.