South Korea’s third largest mobile operator, LG Uplus, launched voice over LTE (VoLTE) roaming with Japan’s KDDI and plans to announce deals with additional foreign operators soon.

The commercial roaming service, which it claims is the world’s first, is only available for customers using LG’s G Flex 2 smartphone in South Korea and Japan. But LG Uplus said it will expand the VoLTE-ready range of devices.

LG Uplus rolled out nationwide LTE in 2012 and said the VoLTE service connects calls in just 0.25 to 2.5 seconds – 20 times faster than 3G. The operator said in a statement that the quality of voice and video calls between Tokyo and Seoul was the same as in the domestic environment.

In late February Japan’s NTT DoCoMo, South Korea’s KT and US-based Verizon Wireless announced they completed VoLTE roaming trials demonstrating HD voice and video calls between different countries.

In October China Mobile, KPN and iBasis said they completed the first international VoLTE roaming call between mobile operators based on IMS local breakout architecture.