http://wccftech.com/iphone-x-no-t-mobile-600mhz-network/

T-Mobile is making massive efforts to roll out its LTE Extended network but even with all the advancements present in the iPhone X and iPhone 8, these devices will not be able to provide support for it. For those wondering, we will provide you with a breakdown of whether this is a setback or if there is something that you genuinely need to worry about before purchasing the iPhone 8 or iPhone X.

To support the new network, both the iPhone X and iPhone 8 need to support Band 71, or the 600MHz spectrum. While the absence of this support will not mean that you will run into compatibility issues with other networks, it does mean that the new LTE Extended network that T-Mobile has been building won’t be accessible to these devices.