Lots of networks blocks VoLTE on the network end if the device is not on their whitelist. Both two of my Xiaomi phones fails to get VoLTE on both networks in my

Lots of networks blocks VoLTE on the network end if the device is not on their whitelist. Both two of my Xiaomi phones fails to get VoLTE on both networks in my country that offers it. Mea while my S21 has no trouble since it is whitelisted with the same two networks that refuse to provide VoLTE to the Xiaomis. Sadly it's a case of making sure you have (1) a VoLTE capable network, (2) a VoLTE capable phone and most importantly (3) a network that whitelists your phone. One network in my country started out only whitelisting only the specific phones they sold (and rejecting phones sold elsewhere even if it's the exact same model, firmware, etc) but I believe they have since loosened up by accepting phones sold by others as long as it's the same model as what they sell themselves. It's a absolute mess and to be honest the only reliable choices are Apple and the last few generations of Samsung phones (as that's what all carriers here sell) but if you stray to other brands it's very hit and miss whether your carrier will support it and worse whether you have the choice of changing carriers to another that also supports your phone. Makes me pine for the good old days of GSM.