this is what i found and why i remembered something about the Apple side.
**Update: Starting with iOS 11, iPhone 6 and newer devices are now enabled with Voice Call Continuity (VCC). VCC allows a call initiated on WiFi to hand off to LTE and back to WiFi, while also permitting the user to access some data functionality. With VCC, a call will never start on LTE so data will be unavailable when a call starts in an LTE area.**
only thing im not sure of is if there have been any changes over the years with either add ons or if for newer phones like the X if it needs to be activated by Apple or if it starts off activated..or if it has it at all anymore.
Voice Call Continuity is built into Apple devices iOS 11, iPhone 6 and newer. It doesn't require activation or opting in.
Keep in mind this isn't a true VoLTE solution, it's a step between nothing and the whole she-bang.
thank yuh ma'am