how to send sms to mobile number on selecting the check box

using System.Text;
using System.IO;
using System.Net;
using System.Net.Sockets;




 string send_url = url;
                Uri uri = new Uri(send_url);
                string data = "field-keywords=ASP.NET 2.0";
                if (uri.Scheme == Uri.UriSchemeHttp)
                {
                    HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(uri);
                    request.Method = WebRequestMethods.Http.Post;
                    request.ContentLength = data.Length;
                    request.ContentType = "application/x-www-form-urlencoded";
                    StreamWriter writer = new StreamWriter(request.GetRequestStream());
                    writer.Write(data);
                    writer.Close();

                    HttpWebResponse response = (HttpWebResponse)request.GetResponse();
                    StreamReader reader = new StreamReader(response.GetResponseStream());
                    string tmp = reader.ReadToEnd();
                    response.Close();
                    conf_sent_sms = tmp.ToString(); 
                }