I have a Pixel 6 Pro and it won't call over WiFi on T-Mobile. A Google developer contacted me after my first one star review, he gave me instructions on how to turn on my WiFi calling in my settings. They were already turned on and yes my carrier is T-Mobile, so they support WiFi calling. I really wish instead of assuming that before assuming that everyone is ignorant, that they could actually investigate what is going on instead of assuming that we don't know how to operate our phones.