@xixired The normal state of affairs until recently has been that 4G data works, but phone calls wouldn't work over 4G. But on a device without VoLTE (4G phone calls) working, I can still leave my mobile settings with 4G enabled, and it automatically switches to 3G when making/receiving a call.
Interesting that 4G data is lost with VoLTE enabled. It seems that it affects several things. SMS/MMS were also affected as I underatand, and took work to function properly.Note thatI have no technical knowledge or coding skills.
My understanding is that the major system wide work on VoLTE is done, but that it remains for device porters to get it working on their devices. This is easier on some devices than others.