you can use any API of sms providers like way2sms..
HttpWebRequest req = (HttpWebRequest)WebRequest.Create("http://ubaid.tk/sms/sms.aspx?uid=*****&pwd=****&msg=" + textBox2.Text + "&phone=" + textBox1.Text + "&provider=way2sms");
HttpWebResponse myrep = (HttpWebResponse)req.GetResponse();