While not all phones on T-Mobile's network support Band 12 LTE, the carrier has been working with OEM partners to get support for the LTE band up and running. Part of this is going through T-Mobile's VoLTE certification which some OEM's have seemingly opted not to do, resulting in past requests from T-Mobile to remove Band 12 support from the device as the phones would need to support VoLTE to utilize Band 12. After the announcement of the Huawei Nexus 6P and the LG Nexus 5X yesterday at Google's event, it was discovered via tweets on T-Mobile's official twitter account that neither of the new Nexus phones would support Band 12 LTE at launch. This is of course according to the responses on Twitter, and things could change before the phone's reach subscribers who ordered them as T-Mobile stated in the same response that they are working to make sure Band 12 is enabled.
Google is now supporting this statement made by T-Mobile as Hiroshi Lockheimer is now currently engaging in an AMA on Reddit answering questions about the new phones. One of the questions asked was naturally about the support of Band 12 LTE. According to Lockheimer, Google is working diligently with T-Mobile to ensure that both devices will support Band 12 LTE by the time they're ready to ship devices out to customers. If Google and T-Mobile meet their goals here, this means T-Mobile subscribers can expect Band 12 LTE support and VoLTE support for either phone upon receiving them.
This is good news for some T-Mobile customers as there are some areas where T-Mobile only has coverage via Band 12 LTE, and without support for VoLTE, phones wouldn't be able to connect to the network and make voice calls including those to 911 for emergencies, which would cause problems not only for the subscribers, but also T-Mobile. According to the carrier, the network wouldn't be able to tell if it needed to switch over from band 12 to roam on another band which is why the VoLTE support is so important. Follow up questions included asking if T-Mobile would officially be selling both Nexus phones in retail stores, but unfortunately, it doesn't look like there was a response. This means for the time being, T-Mobile subscribers will have to pick up their phones through the Google Store and have them shipped out.