https://phys.org/news/2019-02-sprint-5g-network-chicago-atlanta.html

The company plans to launch 5G in Houston, Los Angeles, New York City, Phoenix and Washington during the first half of 2019.

It's unclear how extensive the initial coverage will be in each of the launch cities. Sprint says that the New York launch will be focused on the "nearly 30 square miles covering Midtown and lower Manhattan" while the Dallas launch will cover "approximately 230 square miles spanning the greater Dallas Fort Worth area," suggesting that some cities will be better covered than others.