As the U.S. carriers work to deploy their 5G networks, they're hitting all kinds of milestones as they progress. Today T-Mobile announced that it's hit a major milestone of its own.

T-Mobile has teamed up with Nokia to complete the world's first 5G data transmission on 600MHz spectrum. The testing was performed using downlink transmissions on T-Mobile's live commercial network in Spokane, WA.

T-Mobile has said that it plans to use both 600MHz spectrum and millimeter wave (mmWave) spectrum for its 5G network. There's a big difference between the two, as the high-band mmWave spectrum will offer better capacity while the 600MHz spectrum will reach much farther. T-Mo says that a mmWave 5G site will cover less than one square mile, while a 600MHz 5G site will cover hundreds of square miles.

As for its 5G network rollout, T-Mobile is now in the process of building out 5G coverage in six of the top 10 markets in the U.S., including New York and Los Angeles, as well as hundreds of cities across the U.S. It'll begin offering 5G coverage and 5G smartphones to the public in 2019, and the carrier hopes to have nationwide 5G coverage by in 2020.