AT commands are instructions used to control a modem. Every command line starts with "AT" or "at"
Step 1: Click New Project, then select Visual C# on the left, then Windows and then select Windows Forms Application. Name your project "SendSMS" and then click OK
Step 2: Design your send sms form as below

Step 3: Add a click event handler to the button
private void btnSend_Click(object sender, EventArgs e)
{
try
{
//Using serial port to send sms message
SerialPort sp = new SerialPort();
sp.PortName = txtPort.Text;
sp.Open();
//Using AT command to send sms
sp.WriteLine("AT" + Environment.NewLine);
Thread.Sleep(100);
sp.WriteLine("AT+CMGF=1" + Environment.NewLine);
Thread.Sleep(100);
sp.WriteLine("AT+CSCS=\"GSM\"" + Environment.NewLine);
Thread.Sleep(100);
sp.WriteLine("AT+CMGS=\"" + txtPhoneNumber.Text + "\"" + Environment.NewLine);//Set phone number
Thread.Sleep(100);
sp.WriteLine(txtMessage.Text + Environment.NewLine);//Set messages
Thread.Sleep(100);
sp.Write(new byte[] { 26 }, 0, 1);
Thread.Sleep(100);
var response = sp.ReadExisting();
if (response.Contains("ERROR"))
MessageBox.Show("Send failed !", "Message", MessageBoxButtons.OK, MessageBoxIcon.Information);
else
MessageBox.Show("SMS Sent !", "Message", MessageBoxButtons.OK, MessageBoxIcon.Information);
sp.Close();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message, "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}
After successful connection of the GSM/GPRS modem with your PC, you can send sms message from this application
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