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Whisper it, but most mobile voice calls go over 4G even in places where 5G core networks are activated. That's because wireless carriers have more work to do for voice over 5G to match the maturity and call connection speed of voice over LTE (VoLTE), according to Ookla.

VoLTE, the technology that handles voice calls over 4G, is the "gold standard" today for "consistency and speed" in call setup times, based on test data collected by Ookla's RootMetrics in eight cities around the world, including London, New York, Seoul and Singapore.

Telcos in Seoul delivered the fastest median call setup time (1.06 seconds) on VoLTE, which was speedier than any of the tested voice over new radio (VoNR) implementations, the tech behind 5G calls. Further, 90% of VoLTE calls in Seoul met an important call connection target of under two seconds.

Six out of eight carriers connected calls faster on VoNR versus VoLTE, but the data showed variations in optimization. For example, Singapore's Singtel and Malaysia's Yes clocked faster call setup times on their VoNR deployments than their VoLTE networks. But Singapore's Starhub and Korea's KT VoNR setup times were 32% and 13% slower, respectively, than over VoLTE.

The divergence suggests some carriers have already optimized 5G core networks for voice while others have not.

A reason why voice call connections on 4G are better than 5G is that the older mobile generation has had ten years to mature and for carriers to refine implementations. This, coupled with the slow rollout of 5G standalone (5G SA) core networks, is why most mobile calls today go over 4G networks.

"The vast majority of standard voice calls in developed markets are still going over VoLTE. Even in those markets that have been very proactive on rolling out 5G standalone, in many cases they are still dropping the call back to LTE and not using the full 5G core," said Luke Kehoe, lead analyst at Ookla. "Many operators have tested VoNR over NR and found the performance initially to be subpar relative to VoLTE."

Voice teething troubles are not unique for 5G, as they were also prevalent in the transition to 4G.

"It really is down to the need for more optimization. You're moving to a whole new technology stack ... with a new voice standard, while moving away from something that has been refined and optimized over a decade. That's really the chasm," he said.

Where 5G has been optimized for voice, call connection times are competitive with 4G. However, Kehoe does not think it will take as long for 5G voice quality to improve, given the evidence from operators like Korea Telecom, Singtel and Yes.

"They are getting close to being competitive with the best VoLTE networks already," he said. Looking ahead, 5G voice is expected to be better than 4G with richer calling experiences and higher voice quality. Ookla intends to test other parameters beyond call setup, such as dropped calls.

Voice matters

Ookla tested call setup time because it is a network performance parameter that users notice when it takes too long. The time from pushing the call button to hearing a ringtone should take less than two seconds to feel "instant." Much longer than that, and users are likely to switch to another way to call, like FaceTime or WhatsApp (more often than they already do).

People are making fewer voice calls. In the UK, the number of mobile-originated voice call minutes dropped by 4.6% to 36.84 billion, while calls to landlines decreased 7.2% in the first quarter this year compared to the same period last year, according to Ofcom.

But service quality matters, as Ookla notes persistent, poor voice experience contributes to higher churn and customer complaints.

"Voice is very seldom spoken about in the industry. From an operator perspective, it is absolutely critical that something as basic as this just works. … Getting the calling experience right is really important," said Kehoe.