If I use Wi-Fi calling to make an outside UK call, like to Japan, will it incur any roaming voice call or roaming data charge?
It will incur your normal call charges whatever they are. You will be using your own WiFi, why would there be data roaming charges.
Hi @cklai welcome to the community and thanks for posting. Calls to Japan from your BT mobile are charged at £1.55p/min. As @licquorice mentioned you will incur your normal charges regardless of using wifi calling or not.
Thanks
Neil