AT+SVR AT command is used to set the voice rate coding.
Simcom Module Tutorial
/Voice rate coding command support
/Current setting for voice rate coding
//Set for Full rate/Half Rate
//Set for AMR-HR/AMR-FR/EFR/FR/HR
|Keywords||AT+SVR syntax, examples, parameters, error, input, response.|
With Online AT Command Tester tool, you can test this feature.
With Online AT Command Tester tool, you can also get device diagnostic information easily,