Artemus , Sep 27, 2021 : Settings > Wi-Fi & Network > SIM & Network > SIM # > Enable VoLTE when available.
S1613866683131 , via OnePlus 8T , Sep 28, 2021 : I have check with my carrier and they do support VOLTE on OnePlus 8T, however, i couldn't see the option to enable VOLTE under the sim# tab.
S1613866683131 , via OnePlus 8T , Sep 28, 2021 : I have reach out to OnePlus support and they are working on a solution
