Enviar SMS en C#

SMSMasivos.es: enviar SMS desde C#

public string ConsultarSaldoSMS(string login, string id)
  {
   String parametros = "login=" +
   System.Web.HttpUtility.UrlEncode(login
   ) + "&apiID=" + System.Web.HttpUtility.UrlEncode(id);
   return 
   (HttpPost("http://www.smsmasivos.es/api/credit", 
   parametros));
   }

   public string EnviarSMS(string login, string id, string phone, 
   string text)
   {
       String parametros = "login=" +
        System.Web.HttpUtility.UrlEncode(login) + "&apiID=" 
       + System.Web.HttpUtility.UrlEncode(id) + "&phone_1=" 
       + System.Web.HttpUtility.UrlEncode(phone) + "&text_1=" 
       + System.Web.HttpUtility.UrlEncode(text);
       return 
       (HttpPost("http://www.smsmasivos.es/api/send", 
       parametros));
   }

   string HttpPost(string url, string parametros)
   {
       WebRequest webRequest = WebRequest.Create(url);
      webRequest.ContentType = 
      "application/x-www-form-urlencoded";
      webRequest.Method = "POST";
      byte[] bytes = Encoding.ASCII.GetBytes(parametros);
      Stream os = null;
      try
      { // Enviar Post
         webRequest.ContentLength = bytes.Length;   //Contar bytes a enviar
         os = webRequest.GetRequestStream();
         os.Write (bytes, 0, bytes.Length);         //enviar
      }
      catch (WebException ex)
      {
         return( ex.Message);
      }
      finally
      {
         if (os != null)
         {
            os.Close();
         }
      }
      try
      { // Obtener la Respuesta
         WebResponse webResponse = webRequest.GetResponse();
         if (webResponse == null) 
            { return null; }
         StreamReader sr = new StreamReader 
         (webResponse.GetResponseStream());
         return sr.ReadToEnd ().Trim ();
      }
      catch (WebException ex)
      {
          return (ex.Message);
      }
      return null;
   } 
    }