T-Mobile says that it launched its 5G service in 30 cities, just like it said it'd do way back at the start of 2018. However, T-Mo told LightReading that it's not currently letting any consumers onto the 5G network quite yet since it doesn't have any 5G smartphones that can use it.
T-Mobile previously said that New York City, Dallas, Los Angeles, and Las Vegas would be part of the initial batch of 30 cities that'd get its 5G service. We don't yet know what the other T-Mo 5G cities are, though, nor do we know how much 5G coverage T-Mobile currently has in those cities.
We do know that T-Mobile, like the other three major U.S. carriers, is working on a 5G smartphone with Samsung. Rumors have said that it's a 5G variant of the Galaxy S10 that could launch in the coming months. In fact, a report today said that Samsung's 5G-enabled Galaxy S10 X has a high-end spec sheet that includes a 6.7-inch screen with in-display fingerprint reader, 10GB of RAM, 1TB of storage, and a 5000mAh battery. It's not confirmed that that's the device coming to T-Mobile, but it is a possibility.
Getting back to T-Mobile's 5G network, the carrier has said that it plans to use 600MHz and millimeter wave (mmWave) spectrum for its 5G coverage. T-Mobile has said that it plans to have nationwide 5G coverage by 2020.
UPDATE: T-Mobile has told TmoNews that it's continuing to build out its 5G network in 30 U.S. cities, but the service won't actually launch until 5G devices are available.