Comment by mananaysiempre

From what (little) I understand, VoLTE and VoWiFi are quite similar under the hood—VoLTE is more or less SIP, and VoWiFi is that same SIP over IPsec. You see how this would be an interoperability nightmare (not that I’m excusing the telecom people for getting us into this mess). Furthermore, some carriers get testy about you avoiding roaming charges by using VoWiFi (while others actually encourage it).