How do HD voice calls work? Most of the operators now support HD voice on Android devices. I was wondering about the following points:


How can an Android user be sure that a call is HD without guessing from the audio quality?
Does the phone hand over calls from HD to normal call and vice versa?
None of the carriers in the US support this that I know of. But according to the android supported codec page, AMR-WB (Adaptive Multi-Rate Wideband) is supported by android devices. As long as the carrier is actually using the "spec" to transmit the "HD Voice" over the GSM/CMDA network, there is nothing special that needs to be done for android devices, it will support both Normal and HD calls.

To explain a little further. When an HD call comes in on a device that supports AMR-WB, and it is enabled (based on the comments below that some may not have support enabled), nothing has to be done on the device side. All that is sent to the device is an audio stream, the stream is in the AMR-WB format and the device decodes that automatically. Because it is an audio codec specification and the support for that exists on the device you are able to send/receive using this codec.