Nisu samo operateri krivi. Deo odgovornosti za podršku VoLTE snose i proizvođači uređaja. Iz nekog razloga, neretko ograničavaju VoLTE podršku samo na operatere sa kojima su urađeni testovi. Valjda se plaše lošeg korisničkog iskustva u slučaju da puste VoLTE pa se posle ispostavi da ima problema u radu.
Bio je neki dokument o tome na GSMA portalu, al' ne uspevam sada da ga nađem

Pozdrav
P.S. Našao sam dokument (GSM Association, VoLTE Implementation Guide, July 2023.). Citiram:
"However, a number of practical problems have been reported in the testing of VoLTE/Roaming:
• OEM Blocking of VoLTE – open market devices deliberately disable their VoLTE/IMS capability on insertion of a SIM indicating a network (MCC/MNC) that has not been tested sufficiently. Such blocking is carried out by the OEM to prevent a bad user experience when connecting to an « untested » network and resulting reputational damage to the device. Such blocking also tends to impact to a greater extent on smaller MNOs."