Jul 17, 2005 08:59 AM|Qnnn|LINK
HTTP-based messaging gateways have their own API-s you can use and this far I've seen no complex ones. I got SMS sending work over MxTelecom services after two minutes, so it should be easy enough also for beginners.
Once you get API documentation from gateway provider you can write your code to send requests and process responses. Use WebRequest/HttpWebRequest and WebResponse/HttpWebResponse classes from System.Net namespace."