T-Mobile US launched commercial voice traffic running over its standalone (SA) 5G radio access network (RAN) core in a pair of markets, portending toward a growing push by operators to consolidate their network traffic.

T-Mobile said the commercial voice-over-5G, or “new radio” (VoNR) service, is live in parts of Salt Lake City and Portland, Oregon. It’s planning to roll out the service to “many additional areas this year.”

The technology allows compatible devices in those areas to remain connected to the carrier’s 5G network for both voice and data sessions. The carrier said the service might provide for faster call set-up times, but the real benefit will be in now being able to include voice services as part of its network slicing abilities.

The service is currently limited to the Samsung Galaxy S21 5G device, with plans to add support via the Samsung Galaxy S22 device later this year.

Voice calls are traditionally run over a carrier’s 4G LTE RAN using the well-established voice-over-LTE (VoLTE) standard. For 5G-compatible devices, carriers steer data traffic over their newer networks when it’s available.

This set up requires current 5G devices to also have a 4G LTE radio and antennas to support the voice traffic, which adds cost and complexity to those devices.

The challenge has been in getting voice quality traffic to meet that of legacy systems. Voice traffic is more sensitive to dropped or corrupted data packets than traditional data services.

Standalone 5G is also rare. The 5G core, which enables this framework, allows for a distinct 5G network unencumbered by old equipment, protocols, or standards. 5G isn’t really 5G until it operates in standalone mode.

T-Mobile US activated the world’s first standalone 5G network operating on a 5G core in mid-2020.

In the same year, AT&T anticipated starting the standalone 5G core deployment in late 2020, but it got delayed mainly due to the maturity of the broader ecosystem, AT&T executives claim.

AT&T is still testing its 5G SA core in a lab, and recently stated it was waiting for device maturity before launching commercial services.

“We’ve always said we’re going to deploy this 5G when the ecosystem is ready,” Marachel Knight, SVP of technology and planning operations at AT&T Communications, said during the recent ConnectX event. “Are there devices there to take advantage of that? So, it’s a very methodical approach for us.”

Verizon previously pledged full commercialization of its 5G core in 2021, but it missed that deadline and pushed it back to 2022. However, wireless customers won’t gain access to SA mode on the 5G core until 2023.

Commercial 5G SA services are more common outside of the U.S. This includes all three of China’s largest carriers; Rain in South Africa; Vodafone’s networks in Germany and U.K.; and Telefónica O2 in Germany. Other commercial 5G SA networks include SoftBank in Japan, Rogers in Canada, and Taiwan Mobile.