Hello abhishek . I am using Samsung Galaxy A70 now . I have installed One UI 2.0 Android 10 update in my phone . I am using Airtel sim now . I have used Airtel Wifi Calling service in my Samsung Galaxy A70 phone . Its nice 😀.
VOWIFI uses wifi for calling. If your wifi is slow call quality will not be good. Just like if you mobile data is slow then call via VOLTE wont be good. I am using airtel sim and uses jio in dongle as wifi. and call is good both on VOLTE and VOWIFI.