A:AnswerRecommend doing your research and I've listed some links to help.
WIFI CALLING: https://www.androidheadlines.com/how-to-enable-wifi-calling-galaxy-s20
VoLTE: https://us.community.samsung.com/t5/Galaxy-S20/5G-Volte-Standard-on-S20-5g/td-p/1157225
5G: It works on T-mobiles 5G.
A:AnswerI can tell you the data does not work on the unlocked ones no matter which company you go through. Wifi does work not sure about wifi calling sorry.