This answer describes the solutions of OPPO, Huawei, Xiaomi, Apple, etc. VoLTE HD voice call can be opened in OPPO developers, the following is the specific steps:
OPPOReno8& Huawei P50& Xiaomi 12& iPhone13
ColorOS13 && HarmonyOS3.0 && MIUI13 && iOS16.1
Click System Settings In OPPO's Settings screen, find the system Settings option and click.
Click Developer to enter the system Settings interface, swipe the screen to find the developer option to enter.
Turn on VoNR HD call After switching to the developer interface, find VoNR HD call and turn on the switch at the back.
Tap Mobile Network On the Huawei Settings screen, select Mobile Network and tap.
Click Move Data to switch to the mobile web page, find the Move Data option and click to enter.
Enable VoLTE HD Voice call On the Mobile Data page, find the VoLTE HD voice call, and turn on the switch button on the back.
Click Dual SIM and mobile data to open and enter the Millet setting interface, select dual SIM and mobile data in the system setting interface to enter.
Click Operator to enter the dual card and mobile data page, select operator from the top position to enter.
Enable Enable VoLTE HD call Switch to the SIM card information page, tap Enable VoLTE HD call, and enable the switch button.
Tap Cellular Network In Apple's Settings screen, find the Cellular network option and tap to enter.
Click the Cellular Data option to enter the cellular network interface, find the cellular data option and click to enter.
Click Voice and Data to switch to the Cellular Data options screen, select Voice and data and click.
Enable VoLTE HD voice call Switch to the Voice and Data screen, and find the switch button next to VoLTE to enable VoLTE HD voice call.