I don't think that 48 support WiFi calling but you might need to contact 48 support to ask them.
They certainly didn't a few years ago:
If an attempt to use WiFi calling turns your phone off then that sounds more like a phone issue than a 48 issue.
You might want to check with Apple support and their forums about that.
If you need to contact 48 support about this see the links in my signature below.
