Well, there's my cheapo Nokia 130 (2017) which is GSM only - I understand this to mean that it simply does not have the hardware to connet to 2,3,4,5G networks. How can it then be that "The traditional GSM voice call ... still needs the 2G or 3G cell to work", as you wrote? Does the GSM network itself rely on 2/3G, even if the phones using it don't? I had a look at what peterleinchen linked but I still don't get it.