C # Bina with Usb Fax Modem

I would like to know a way to get the phone number of a usb fax modem, using C# .

Example: I have a computer with a fax modem usb connected to a phone line, when someone calls me my system picks up the number which is meligando and places in textbox .

I am trying with SerialPort as follows:

public void GetNumber() {

    serialPort.PortName = cbPorta.Text;
    serialPort.BaudRate = Convert.ToInt32(cbTxTransmissao.Text);
    serialPort.Handshake = Handshake.None;
    serialPort.Parity = Parity.None;
    serialPort.Open();            
    var Comando= Encoding.ASCII.GetBytes("AT&Zn?");
    serialPort.WriteLine(Comando);
    System.Threading.Thread.Sleep(200);
   lbStatus.Text = serialPort.ReadLine();
   serialPort.Close();
}