VoLTE is one of the words you will have heard and read a lot about over the last year and even more so if you are a T-Mobile customer. As the ability to make use of Voice over LTE is likely to be an aspect which will greater improve your call experience. That said, if you are a T-Mobile customer, then to make use of VoLTE, you do need to have a device which is compatible with T-Mobile's band 12. An aspect which seems to have been problematic for a number of devices so far, both old and new and even including the likes of Google's Nexus 5X and Nexus 6P.
The issue arises from the certification T-Mobile needs devices to have to make use of band 12 and as a result T-Mobile kindly did ask manufacturers to remove the support for band 12 while awaiting certification. This included the Nexus 5X and 6P and in spite of Google stating that the two Nexus devices will support T-Mobile's band 12 by the shipping date. In fact, the latest on this issue came a few weeks ago when T-Mobile announced that they were still working on the issue, although at the time they failed to provide any concrete information on when it would likely be ready. And this was again in spite of the Nexus 6P suddenly listing band 12 support on the T-Mobile support pages.
Well, today saw Google release the latest update for Nexus devices in the form of Android 6.0.1 (Marshmallow). An update which saw the factory images become available for most Nexus devices including the 5X and 6P. Since then, reports are steadily coming in that the update seems to bring with it support for band 12 on T-Mobile. At the moment, there has not been any official word from either T-Mobile or Google on band 12 and the update, although, the support does seem to be included. For now, once the update does begin a more widespread roll out and lands on more devices, it is likely that more reports will make it clearer as to whether the support has been fully activated. Although, for now, it does seem that the latest Nexus update is bringing with it support for band 12.