What does it mean that HD appears in front of the cell phone signal?

HD is high definition voice, which is a free upgrade of ordinary telephone service.

VoLTE service, like making phone calls and sending short messages, is a free basic service function that numbers automatically enjoy, and operators will not charge any function fees.

This kind of high-definition voice can make the user's voice clearer and dial faster when making a phone call, and if the user often uses his mobile phone to surf the Internet, he can also surf the Internet while making a phone call without interfering with each other.

Extended data:

The most direct feeling brought by VoLTE technology to 4G users is shorter connection waiting time, higher quality and more natural voice and video call effect. VoLTE is essentially different from 2G and 3G voice calls. VoLTE is an end-to-end voice solution based on all IP in 4G network.

Compared with 2G and 3G voice calls, VoLTE can improve the voice quality by about 40% due to the adoption of high-resolution coding and decoding technology. VoLTE brings users a lower access delay (waiting time after dialing), which is 50% lower than that of 3G, about 2 seconds, compared with 6-7 seconds in the 2G era. In addition, under 2G and 3G, dropped calls sometimes occur, but the dropped call rate of VoLTE is close to zero.

Baidu encyclopedia -VOLTE