Hi there! We understand how important it is for you to know when we will support Wi-Fi Calling on the OnePlus 8T. At this time, the OnePlus 8T doesn't support Wi-Fi Calling on the Visible network. As Visible is growing, we're working hard to improve our offerings, and more devices are being added to our confirmed list. We currently don't have a specific date but our best recommendation is to continuously check our website for any updates.
Thanks for reaching out and being the best part of Visible! -WC