System.Net.WebRequest reqPOST = System.Net.WebRequest.Create(@"http://web.mirsms.ru/public/http/");
                reqPOST.Method = "POST"; // Устанавливаем метод передачи данных в POST
                reqPOST.Timeout = 120000; // Устанавливаем таймаут соединения
                reqPOST.ContentType = "application/x-www-form-urlencoded;"; // указываем тип контента

                byte[] sentData = Encoding.UTF8.GetBytes
                    (
                        "[user]=>" + "111" +
                        "[password]=>" + "111" +
                        "[action]=>" + "post_sms" +
                        "[message]=>" + "Текст сообщения" +
                        "[target]=>" + "111" +
                        "[post_id]=>" + "123" +
                        "[period]=>" + "60" +
                        "[CLIENTADR]=>" + "127.0.0.1"
                        
                    );

                reqPOST.ContentLength = sentData.Length;
                System.IO.Stream sendStream = reqPOST.GetRequestStream();
                sendStream.Write(sentData, 0, sentData.Length);
                sendStream.Close();

                System.Net.WebResponse result = reqPOST.GetResponse();
                Stream s = result.GetResponseStream();

                StreamReader sr = new StreamReader(s);
                string str = sr.ReadToEnd();