public string send_sms()
{
string str_userid = "ID";
string str_account = "账号";
string str_password = "密码";
string str_content = "内容";
string str_mobile = "手机号码";//130xxxxxxxx,131xxxxxxxx多个号码用英文半角‘,’分隔

string param = string.Format(@"action=send&userid={0}&account={1}&password={2}&content={3}&mobile={4}", str_userid, str_account, str_password, str_content, str_mobile);
string url = "http://sms.kingtto.com:9999/sms.aspx";
Response.Write(PostSend(url, param));//输出返回值
}

private string PostSend(string url, string postdate)
{
HttpWebRequest myHttpWebRequest = (HttpWebRequest)WebRequest.Create(url);
myHttpWebRequest.ContentType = "application/x-www-form-urlencoded;charset=UTF-8";
myHttpWebRequest.Method = "POST";
Stream myRequestStream = myHttpWebRequest.GetRequestStream();
StreamWriter myStreamWriter = new StreamWriter(myRequestStream);
myStreamWriter.Write(postdate);
myStreamWriter.Flush();
myStreamWriter.Close();
myRequestStream.Close();

HttpWebResponse myHttpWebResponse = (HttpWebResponse)myHttpWebRequest.GetResponse();
Stream myResponseStream = myHttpWebResponse.GetResponseStream();
StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8"));
String outdata = myStreamReader.ReadToEnd();
myStreamReader.Close();
myResponseStream.Close();
return outdata;
}