If you find that your call quality isn't as good as it should be, here are a few things you can try.
Check your phone is compatible with WiFi Calling. If your device isn't on this list, then its the device (rather than SMARTY) that doesn't support WIFI calling so perhaps think about upgrading your phone.
Ensure that WiFi is enabled on your phone.
Check that you’re connected to a WiFi network.
If you’re connected to a WiFi network, check that you can access the internet by trying different webpages.
Check your device to ensure you see the WiFi symbol. If this doesn’t show, you’re not connected to WiFi.
If your device shows that you’re connected to WiFi, try restarting the router, as the issue may be with your WiFi connection.
Remember, if you move between WiFi hotspots, this can sometimes cause disruption to your call.