Now, this is not a definitive proof and doesn’t give any hint whatsoever about timelines of when it will come to Windows Phone. Even on Android, it still is invitation based and you need a call from someone on WhatsApp, with this calling feature enabled on their Android devices. The latest WhatsApp build has brought this feature to Android devices, so Windows Phone fans hopefully may not need to wait a lot.
Thanks Martin23 for the tip. Cheers!!