I’m using /e/OS with Murena Two and Bouygues Telecom provider in France.
In 4G as preferred network (the default setting), SMS are all received but all fail to send, and Visual Voice Mail is activated but reports that it is not fully configured (but Bouygues Telecom does not offer any setting to configure it).
Although this is not satisfying, I found a temporary workaround to these 2 issues by disabling 4G in Parameters > Network and Internet > SIM profile > Preferred network type > 3G. Then VVM and SMS started working by themselves immediately.
Correction: after I switch to 3G, it works for sending a single SMS, and then fails again for later ones. Switching to 4G and then 3G again allows to send a single message and fails again. But VVM keeps working now.
I reactivated Wifi calling and VoLTE a couple of hours ago when I saw your question.
So far it’s working very well for both SMS and calls so I think that the issue is fixed. I run /e/OS 1.21.
@yoan Thank you for the information. Yes, I just recently (~3 day ago, or so) updated to v1.21. Must check this and confirm. Will come back and report when ready.