https://www.cnet.com/news/t-mobile-goes-all-in-on-5g-buildout-with-3-5b-nokia-deal/

But lest you think the agreement means T-Mobile no longer needs to join with Sprint to make its 5G dreams come true, Neville Ray, Chief Technology Officer for T-Mobile said in the news release "We are all in on 5G...And together with Sprint, we'll be able to do So. Much. More."

The deal includes 600 MHz and 28 GHz millimeter wave 5G NR capabilities. (Don't know what that means? Here's an explainer.) You still won't be able to use it until 2019; the company's holding off until the 5G-capable phones start rolling out.