Every mobile network has its own IMS and Bin profile for VoLTE and VoWiFi services. Sometimes mobile manufacturers do not add support of every network in the world in every country's update. Some times they only add support of that network only to update of that specific country. Like after one ui 6 all Pakistani devices got Ufone VoLTE support which was missing earlier. But devices with other region working in Pakistan as CPID approved didn't get Ufone VoLTE support even after one ui 6 and december security update.
