Yes, the mobile 4G brand of YTL Communications in Malaysia, said that it and Singapore’s TPG Telecom emerged as the first telecommunications providers in SouthEast Asia to launch VoLTE roaming. TPG Singapore was the first in SEA to launch outbound VoLTE roaming, with Yes complementing as the first network in Malaysia to open inbound VoLTE roaming traffic from TPG Singapore.
Yes says it was the first Malaysian mobile operator to launch VoLTE service nationwide in June 2016 and remains Malaysia’s only all-IP, all-LTE network provider.
Source: https://www.telecompaper.com/news/yes-tpg-launch-southeast-asias-first-volte-roaming--1309974