More than 300 million consumers will be using voice over LTE by the end of 2016, new research has claimed.
A report from IHS revealed that there were 23 VoLTE networks launched in the first four months of 2016, as many as were launched during 2014 as a whole. Last year, 40 VoLTE networks went live.
The bulk of the 185 million VoLTE users that existed by the end of 2015 came from Japan, South Korea and the United States.
Stéphane Téral, Senior Research Director at IHS, said operators were offering the service as a free upgrade, rather than a subscription service.
He cited Verizon's Advanced Calling, where consumers buy a VoLTE compatible handset and are automatically connected to the service, as an example.
However, Téral added while there are 500 commercial LTE networks globally, issues remain with implementing the technology effectively.
He said: "Making VoLTE work perfectly with no glitches remains challenging, and service providers know they need to achieve a degree of LTE network ubiquity and then beef up their IP multimedia subsystem (IMS) infrastructures to fully support VoLTE. But in the meantime, the VoLTE frontrunners are ramping up VoLTE users."
He added challenges also surround ensuring VoLTE users can roam effectively, with indecision around whether local breakout or S8 home routing technology is the best format.
IHS has predicted that service revenue from VoLTE will reach $6.3 billion, with almost half of that money coming from the ARPU-rich United States.
However, Asia Pacific will have three times as many VoLTE users as the United States, largely driven by China Mobile's continued aggressive push of LTE and related technologies.