@mike2717 At times you do need to contact your provider. However as well as the quick settings should check in phone,Menu(3 dots)- Settings-Wifi Calling. May need to toggle it on for activation. Visual guide in this article https://www.samsung.com/uk/support/mobile-devices/how-to-activate-wifi-calling-on-a-galaxy-smartphon...
I do not work for Samsung or make Samsung Products but provide independent advice and valuable contributions.
My Device- S21 Ultra 5G ( SM-998B/DS ) CSC= BTU , 12GB/256GB
One Ui 5.0,Android 13 .