I use Wi-Fi calling on a phone only for 2FA SMS. Never had a problem with it. It was RedPocket (MVNO) with T-Mobile. Annual plan of 200MB, only a few dollars a month. No T-Mobile service here* so only SMS over Wi-Fi works. Only ever used for SMS 2FA.

*The bands acquired with the Sprint merger have service, but the cheap used phone I bought was pre-Sprint-merger and lacked those bands.