alt Hacker NewsI was under the impression WiFi Calling was just regular phone service through WiFi. It seems to work that way for me, 2FA codes and all.
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tim333 • yesterday at 10:44 AM
WiFi calling seems to depend on your mobile service provider to provide the service. I guess different networks do it differently.
VoWiFi (as Wi-Fi calling is called in the 3GPP specs) is similar to VoLTE, but not all SMS go over VoLTE: Unlike for calls, where there's mandatory VoIP in 4G/LTE and beyond (there is no more circuit switching), there's still a fallback path for SMS that uses legacy signalling instead of IMS (which powers VoWiFi and VoLTE/VoNR).
Maybe there are some SMS gateways that are somehow incompatible with some IMS message gateways? (Theoretically, the IM-SM-GW should be transparent to external networks, I believe, but practically I wouldn't be surprised if some weird things lurked in there, requiring a fallback to the signalling path, which is not available on VoWiFi.)