777SAO, May 24, 2019 : I've been searching all around, called my Carrier support, opened a Bug report on OnePlus for this issue posted around the forum, no one was able to help. I even have a thread (where i will link this one) asking people with whom it worked and didn't work... and now i found the solution. I just tested on my 7pro, and it worked! Follow this link and the article, and report back to see if it works! https://www.theandroidsoul.com/how-to-enable-volte-and-vowifi-on-oneplus-7-pro/ I'll be happy to know if i helped some people!