No date as of yet, and while the majority of devices do come with WiFi calling, some will still require updates!
I have successfully gotten The tmobile Wifi calling working on my new Oneplus cell phone. I took down a older Tmobile APK file (think from XDA Developers web site. The signal was nothing due to when I was and I had the phone on airplane mode. I set the software switch (in settings) and run the Wifi app, It works!
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