The BYOD Check App checks the potential compatibility of a device with T-Mobile’s Extended Range LTE and Voice Over LTE network technologies.
T-Mobile’s Extended Range LTE goes 2X as far and penetrates walls for 4X better indoor coverage, while Voice Over LTE gives our customer the best voice call quality in our network.
This app is currently in beta version, may contain unresolved inaccuracies, and should not be relied on by current or prospective customers. T-Mobile cannot and does not guarantee the functionality or performance of any handsets or devices that were not sold by T-Mobile or an authorized dealer of T-Mobile ("Non-T-Mobile Devices") for use on the T-Mobile network, or that do not have a software version sold or updated by T-Mobile (e.g., rooted devices). We are not able to test Non-T-Mobile Devices’ call quality, performance, data speed, feature compatibility, or other functionalities, so please be aware some experiences may vary greatly depending on, e.g., the settings from the customer’s original carrier. We strongly recommend that customers contact the manufacturers of their Non-T-Mobile Devices with any questions or problems regarding the functionality, operation, or performance of their Non-T-Mobile Devices.  Customers should check their warranty and contract with their current carrier to see what conditions apply to unlocking their device. Coverage not available in some areas.
From version T-Mobile BYOD Check App 1.0.8:
Minor text fixes
Updated data set
All versions
November 17, 2017