I had implemented a project where SMS text was generated after user selects some text and forwarded it to mobile numbers fetched from database.
The SMS gateway provider gave us a URL in which the SMS text and the mobile numbers were embedded as parameter values , something like below
string url =@"http://10.10.10.10/id=ourId&password=xyz&message="+smsText+"&mobileNum="+num[i];
This string string contained url which was called using WebClient class
using (WebClient client = new WebClient())
{
client.DownloadString(url);
}