Step 1: Create a new project called SmsMessages
Step 2: Design your form as below

Add code to handle btnSend event click
private void btnSend_Click(object sender, EventArgs e)
{
try
{
WebClient client = new WebClient();
//Call web api to send sms messages
Stream s = client.OpenRead(string.Format("http://api.clickatell.com/http/sendmsg?user=YOUR USERNAME&password=YOUR PASSWORD&api_id=YOUR ID&to={0}&text={1}", txtTo.Text, txtMessage.Text));
StreamReader reader = new StreamReader(s);
string result = reader.ReadToEnd();
MessageBox.Show(result, "Message", MessageBoxButtons.OK, MessageBoxIcon.Information);
}
catch (Exception ex)
{
MessageBox.Show(ex.Message, "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}
To play demo, you need to create an account at clickatell website
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