How to enable default speaker and mic of my laptop when call is established

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Hi I have following code to make phone call using at commands in c# phone using gsm modem. Call successfully establish but when I receive call no voice hear nothing happened. Question is how to enable my laptop mic and speaker when phone call is establish the default software of my gsm modem is supported voice call I'm successfully make and receive phone call with default software of my gsm modem here is my code

System.IO.Ports.SerialPort comPort;
comPort = new System.IO.Ports.SerialPort("COM17", 115200, System.IO.Ports.Parity.None, 8, StopBits.One);
comPort.Open();
comPort.DtrEnable = true;

//Switch to Voice Mode
comPort.Write("AT+FCLASS=8" + System.Convert.ToChar(13).ToString());

//Call Number
comPort.Write("ATD+123456789;" + System.Convert.ToChar(13).ToString());
System.Threading.Thread.Sleep(17000);

//Enter Voice-Transmission Mode
comPort.Write("AT+VTX" + System.Convert.ToChar(13).ToString());