As BGR points out, the specs page for Apple’s new iPhones shows that the phones will support the usual North American LTE bands, all except for Band 71 which is what T-Mobile’s new LTE network will use. Given how much the new iPhone X is priced (starting at $999), buying a phone that can’t take full advantage of what your carrier has to offer doesn’t seem like a good use of your money, and no doubt this will affect sales of the handset, although exactly by how much remains to be seen.
According to BGR’s report, T-Mobile only managed to secure the 600MHz license earlier this year, which means that there might not have been enough time to build Band 71 into the iPhone’s modems. However it is unclear if this could be rectified in the future via a software update, if not we guess T-Mobile customers will either have to contend with missing out on the new network, or they’ll have to find another phone, or maybe even jump ship to a different carrier.