> If you have an old phone, that doesn't support VoLTE (including for emergency calls), then it will only connect to 4G networks in areas where there is still an overlapping 2G/3G layer.

I guess the question is, how do they determine if a phone doesn't support VoLTE for emergency calls? That seems to be the problem in Australia, that there is no reliable way to detect it, so they're just using crude whitelists.