The symbol described by the subject means HD call.
HD is VoLTE, and its biggest role is that voice calls are no longer carried by 2G GSM\/CDMA networks, but use 4G networks to transmit voice data.
4G networks have higher bandwidth and support more advanced voice coding technology, and call quality will be significantly improved. So we call it HD voice calling.
Another advantage is that when we talk, the network no longer disconnects and falls back to the 2G network. Internet service is still normal, you can make phone calls while surfing the Internet.