With Wifi Calling you can also just text. 🙂
I know that some discount carriers do not support WiFi calling, but what modern phones do not?
The vast majority of people can use Wifi calling. But yes, for those few who cannot, Whatapp, or Skype, or Messenger, or Kik, or Imo, or Viber, or...... work fine. The only issue is, the person on the other end needs to be using the same app.