C#

private void button1_Click(object sender, EventArgs e)
        {
            for (int j = 0; j < 3; j++)
            {
                i = j;
                myCurThread = new Thread(new ThreadStart(myThread));
                myCurThread.Start();
                myCurThread.Join();
            }
        }

private void myThread()
        {
            string result = "";
            myComport = new ComPort();
            
            myComport.Device = "COM5";
            myComport.BaudRate = 115200;
            myComport.HardwareFlowControl = myComport.asFLOWCONTROL_ENABLE;
            myComport.DataBits = (short)myComport.asDATABITS_DEFAULT;
            myComport.StopBits = (short)myComport.asSTOPBITS_DEFAULT;
            myComport.Parity = (short)myComport.asPARITY_DEFAULT;

            myComport.ComTimeout = 8000;
            myComport.Open();

            string strUSSD = "AT+CUSD=1,\"" + "*444#" + "\",15";

            myComport.WriteString(strUSSD);

            if (myComport.LastError == 0)
            {
                result = myComport.ReadString();
                while(result.IndexOf("Result") == -1)
                {
                    result = myComport.ReadString();
                    Debug.WriteLine("i = " + i + " " + result);
                }
            }

            myComport.Close();
        }