i just check that i CAN still make calls on 2G in 4.6.0.15 on my 10 III (and can connect to mobile data on 2.5G) when i select “2G-only” and disable “4G calling”.
i confirmed that the call was definitely not VoLTE. this is on t-mobile in ny, usa. (i cannot test 3G, since there is no 3G here anymore)