Tak for det erik, det virker nu :)
Her er koden til det, hvis der er nogen som kan bruge det.
byte[] buffer = Encoding.ASCII.GetBytes("username=XXX&password=XXX&message=XXX");
HttpWebRequest WebReq = (HttpWebRequest)WebRequest.Create("
http://sms.coolsmsc.dk:8080/sendsms.php?username=XXX&password=XXX&message=XXX");
WebReq.Method = "POST";
WebReq.ContentLength = buffer.Length;
Stream PostData = WebReq.GetRequestStream();
PostData.Write(buffer, 0, buffer.Length);
PostData.Close();
HttpWebResponse WebResp = (HttpWebResponse)WebReq.GetResponse();
Console.WriteLine(WebResp.StatusCode);
Console.WriteLine(WebResp.Server);
Stream Answer = WebResp.GetResponseStream();
StreamReader _Answer = new StreamReader(Answer);
Console.WriteLine(_Answer.ReadToEnd());