"We want to be a 5G-only business," T-Mobile's networking chief, Neville Ray, said during an appearance at an investor event Friday.

T-Mobile took a big step toward that goal Friday by shutting down Sprint's aging 3G CDMA network and concurrently shifting some of T-Mobile's voice traffic onto its growing 5G network, Ray said. The move to introduce Voice over 5G New Radio technology, or VoNR, puts T-Mobile on the bleeding edge of 5G, considering the vast majority of 5G network operators across the globe haven't yet commercially added VoNR.

However, Ray declined to speculate when T-Mobile would fully complete its shift away from 3G and 4G in order to operate solely on 5G.

"We're driving hard to that 5G vision," he said. "We're really pushing the 5G envelope."

Figure 1: (Source: Robert K. Chin - Storefronts/Alamy Stock Photo)

Voice calling over 5G

T-Mobile said it is offering VoNR in "limited areas" of Portland, Oregon, and Salt Lake City and plans to expand the service to more areas this year and next. The service is currently available only on the Samsung Galaxy S21 smartphone.

Ray credited T-Mobile vendors including Nokia, Ericsson, Qualcomm and Samsung for the launch. He said 5G VoNR call setup times will be faster than on 4G, but the call quality will be relatively similar to 4G Voice over LTE, or VoLTE.

VoNR requires the "standalone" version of 5G. T-Mobile launched Standalone (SA) 5G almost two years ago. Both Verizon and AT&T had planned to launch the SA version of 5G in 2020, but neither has yet done so. Verizon has said it expects to begin moving traffic onto its SA core later this year, but AT&T has provided no firm SA launch date.

Calling Dish

T-Mobile joins Dish Network in launching VoNR. However, Dish doesn't operate a 4G network.

Dish officials said in February that the company has struggled to implement VoNR, partly due to the complexities involved in supporting emergency services like 911.

However, in a recent conversation with Light Reading, Dish's Sidd Chenumolu, VP of technology development, said that the company has rolled out VoNR onto its 5G network. Chenumolu explained that the operator views VoNR as another data service running on top of the network. He added that it would be relatively easy for Dish to introduce other voice calling protocols, such as Microsoft Teams, on top of its network, if customers want such services.

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— Mike Dano, Editorial Director, 5G & Mobile Strategies, Light Reading | @mikeddano