SMS messaging from a webpage

I am trying to send sms messages from a webpage on a site that I am creating. I am using the clickatell sms gateway. They provide a C# example API on their site which looks like this.

using System.Net;
using System.IO;
WebClient client = new WebClient ();
// Add a user agent header in case the requested URI contains a query.
client.Headers.Add ("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR
1.0.3705;)");
client.QueryString.Add("user", "xxxx");
client.QueryString.Add("password", "xxxx");
client.QueryString.Add("api_id", "xxxx");
client.QueryString.Add("to", "xxxx");
client.QueryString.Add("text", "This is an example message");
string baseurl ="http://api.clickatell.com/http/sendmsg";
Stream data = client.OpenRead(baseurl);
StreamReader reader = new StreamRe ...