In the code behind file, we need to copy and paste the API code provided by the SMS Gateway. As I already explained, every SMS Gateway service provider provides the API code to be used in your application. In mvaayoo, they provide the API code for ASP.Net, ASP, VB and PHP too. You need to substitute the user name password and sender id in the respective places in the URL. You need to also specify the mobile number too in the URL. If you want to send the SMS to multiple numbers then you need to provide those numbers in comma-separated format.