The status bar displays a high-definition sign, indicating that the mobile phone card has been successfully registered for high-definition voice calls, HD 1 indicates that the card 1 is online, HD2 indicates that the card 2 is online, and HD 12 indicates that both mobile phone cards have been registered for high-definition voice calls.

Introduction of VoLTE: VoLTE is based on 4G network, and through IP transmission technology, operators can realize the unified bearing of data services, voice calls, video calls and short/multimedia messages services. Under the VoLTE network, the voice call quality is better and clearer, the call waiting time is shorter (the connection time is as short as 3 seconds), and you can surf the Internet while talking, and the data network will not be disconnected. The daily use of the VoLTE function will make the communication experience better.

How to turn on VoLTE: At present, the system turns on VoLTE HD calling function by default, and there is no setting option. Just contact the operator to open the VoLTE service, which can be used under the coverage of VoLTE network.

The contact numbers of the four major domestic operators are: 10099 (China Radio and Television), 10086 (China Mobile),10 (China Unicom) and 10000 (China Telecom), so you can call them in time.

1.Funtouch OS 9 and above system models: Enter Settings-Mobile Network/Dual Card and Mobile Network-Mobile/Unicom/Telecom-VoLTE HD Voice Call.

Note: If this option is not available, it is turned on by default.

Second, how to turn on the following system models of Funtouch OS 9:

Path 1: Go to Settings-More Settings-About Mobile Phone Status-SIM Card, just open "VoLTE Call";

Path 2: Enter Settings-Telephone and turn on "VoLTE Call".

If there is no VoLTE switch in the settings or you have more questions, you can go to vivo official website-My-Online Customer Service-Sliding Bottom-Online Customer Service-and enter the manual customer service for consultation.