T-Mobile US announced at CES in Las Vegas new tests of 5G services in the 600 MHz band, according Telecompaper. With Intel and Ericsson, the carrier conducted the world’s first 5G data call and video call on 600 MHz spectrum, including successful uplink and downlink communication, on a live commercial network.
During the tests, the teams generated a 5G signal capable of covering more than a thousand square miles from a single tower. T-Mobile also accomplished a tri-band 5G video call with three users on different spectrum bands – 600 MHz, 28 GHz and 39 GHz. 
T-Mobile started testing 5G on its live network in the 600 MHz band in late 2018, in cooperation with Nokia. The operator said the 600 MHz band will be key for the roll-out of 5G due to its ability to cover long distances and penetrate into buildings. This contrasts with the strategy of its main rivals Verizon and AT&T, which are focusing on high-band spectrum for the first 5G services.
T-Mobile is already rolling out what it calls Extended Range LTE in the 600 MHz band, which is already live in more than 1,500 cities and towns in 37 states and Puerto Rico. The company aims to have nationwide 5G coverage by the end of 2020. 
The latest tests with Ericsson used the Intel 5G Mobile Trial Platform. T-Mobile signed framework contracts with Nokia and Ericsson in 2018 for the roll-out of its 5G network.