Owners of the Nexus 6P on T-Mobile's network should prepare themselves for a software update that will enable the handset's band 12 support.
On the carrier's dedicated page for Extended Range LTE (700MHz spectrum), T-Mobile listed the Nexus 6P as one of the devices compatible. But being compatible does not mean that the handset is operating on band 12 at the moment. Google will need to push a software update to the Nexus 6P that will activate functionality. It's very likely that band 12 support for the Nexus 6P is included with Google's next security update for all Nexus devices.
The Nexus 5X has not been listed by T-Mobile; however, that does not rule out its chance to receive a software update activating band 12 support.
Band 12 support is very important for consumers because it allows them to expect solid coverage in buildings and rural areas. Just ask buyers of the OnePlus X how disappointed they are about OnePlus' decision to not include band 12 support.
Source: T-Mobile
Via: /r/Android
That page now says this:
Google*
Google Nexus 6P
Google Nexus 6
Google Nexus 5X
*We’re working with Google to test Extended Range LTE and VoLTE on the Nexus devices -6P, 5X, 6, and will have more to share soon.