Iinm all telcos in Malaysia now supports WiFi Calling
Digi Celcom Maxis U Mobile Yes Unifi Mobile
Several Yes users (including me on 2023 Oct - Nov) got WiFi Calling already

unifi Mobile and Yes allow overseas IP (CMHK) , Digi allows overseas IP (Chunghwa Telecom / Singtel) , U Mobile allows overseas IP based on whitelisted ASN (e.g. China ISP have their own AS Number based on their province or city, these AS number might not be whitelisted by U Mobile and reject for register on IMS)