T-Mobile announced in a press release that they will be deploying LTE-U technology in Spring of 2017. This is the next evolution in LTE, and while it's not quite 5G, it will allow for more bandwidth for users on their network. LTE-U uses unlicensed spectrum, typically around 4-5GHz. According to T-Mobile, LTE-U will allow the Un-Carrier to bring their upcoming Gigabit LTE to even more markets around the country. In the Spring, T-Mobile users will be able to start using the first 20MHz of 5GHz spectrum on LTE-U. It won't be replacing band 12 or any of the other bands that T-Mobile uses for their LTE network right now. This is going to be in addition to those bands, allowing for more capacity.
The announcement from T-Mobile also talks about how the FCC has approved the first LTE-U hardware from their partners - Ericsson and Nokia. These two companies are responsible for the majority of the hardware in use today in mobile networks - Huawei is also responsible for it, but not as large of a player in the US. T-Mobile actually began field testing LTE-U equipment back in December of 2016. And now they are getting ready to roll it out to more places and open it up to T-Mobile customers.
Many may wonder what this means for T-Mobile customers, well this means that you'll be able to see faster data speeds, especially during peak times (like during the morning and evening rush hours). This also means that as T-Mobile continues to grow and add more and more customers and connections, that their network speeds won't diminish and they'll stay at the top of their game. But for the most part, this won't affect T-Mobile customers, it'll just make their experience on the magenta network all that much better. And it's a network that is already pretty strong, according to multiple crowdsourced reports, like OpenSignal, Ookla and others. T-Mobile says that they will be the first with LTE-U in their network, when it launches in the Spring, and yes you'll most likely need a new device to take advantage of it, unfortunately, but that's how it goes when new bands are added to a network.