Allow me to clarify my original point.
I think international wifi calling (from domestic to international) will not probably change. It can but not by much.
The bigger question that I have is wifi calling from international and whether this will be charged international roaming or not.
Because I'll tell you that runs up VERY quickly, especially when you don't rent a phone.
I would bet calling from your US based number to an international number while international (ie, call hotel in Ireland while in Ireland from your Sprint WiFi phone) would cost $$ still.
sent from an underwater dust storm with my Sprint S5