This is of-course a big question and neither the service provider nor the brand has any clear answer for it. I want to show some example and ask sony for a clear picture. Find the three images attached, which I took from JIO 4G website. In the first one, I test the JIO sim compatibility for Samsung Mobile and Almost all the models show 4G VoLTE compatible. In the third image, it's Sony XPERIA XA Ultra which shows it only supports 4G LTE, not 4G VoLTE. At first, I thought may be Sony has no such provision but then, I found the second image which clearly shows that Sony XPERIA XZ has this feature. So the big question is why Sony XPERIA XA Ulta can not have this feature whereas Samsung 10-15K phones can have... ???!!!!... FYI: Earlier the Samsung models had no 4G VoLTE. They got after a software update. I am using one. It's time for Sony to try rather than just blaming on operators.
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