T-Mobile US demonstrated 5G smartphones will be capable of operating on FDD spectrum after completing a low-band test on a commercial next-generation modem.

The FDD capability could prove crucial to 5G deployments in the US, with many operators in the country planning to use the spectrum as they recycle 3G and 4G airwaves for the latest technology.

It teamed with Qualcomm and Ericsson on the test, using the latter’s radio equipment and the former’s X55 modem and RF components in a prototype handset. Testing took place in T-Mobile’s lab in Washington state and ran on the 600MHz spectrum it is planning to use for nationwide 5G deployments later this year.

The trio didn’t share any metrics from the trial, however Qualcomm president Cristiano Amon said in a statement the achievement paves the way for commercial launches of low-band networks and devices, demonstrating “the ability to dramatically increase 5G’s global footprint”.

Qualcomm’s original X50 modem powered the first wave of 5G devices which debuted in the first half of this year, but lacked FDD compatibility. Those capabilities were added when the X55 launched in February.

Executives from both AT&T and T-Mobile previously told Mobile World Live they expect low-band compatible 5G handsets to launch in the second half of 2019.