Well, SMS over WiFi is a part of the VoWiFi standard, despite the V. That said, MMS over WiFi is not part of the VoWiFi standard and is supported carrier by carrier. Mine supports it.
But, yes, it’s moot in this case.
Fair enough, but it’s doubtful that the mobile carrier would be able to change the wifi settings you’ve entered on your phone, even if they can update their mobile network settings OTA, and even if the provider of mobile service and home internet is the same.
FYI - problem solved for today 
and my L5 has VoLTE “enabled”.
Mi history with Rogers started about last January, and I have to call the, tooo many times (about 9 times a week) because everything was headed south - and from chats with techs there, Rogers is fixing, tweaking, changing things - to me it’s been a nightmare of being on a plane that is crashing in to a train wreck. .. It is really hard to try to maintain and privacy.
Thanks for chiming in,
~s
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Doubtful, yes. Doubtful until it happens. 
If the providers are the same and the provider is a fascist that controls the modem/router’s settings (as is likely the case for me and seems to be the case for the OP) then the WiFi settings on the wireless access point inside the modem/router almost certainly can be changed remotely by the provider, which has the effect of changing the WiFi settings on all client devices, in the sense of potentially making the client device not work any more or making the client device work differently.
As an illustration, it may be possible to conduct a downgrade attack against the client device by downgrading the security protocol version on the modem/router if the client device is configured to accept all earlier protocol versions.
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