We have out of box notification methods like: email, fax, pager email and notification.
All of these have a pre-defined code which does the job of routing the notification from ServiceDesk to the respective servers depending on the notification. If we need to create an SMS notification we need to create a custom notification method by clicking Notification method under notifications node and then click 'create new', in the notification method tab we would mention the path of the batch file which has the code for routing it to the SMS server and the SMS server would take it from there.
Example notification method would be: Launchit c\applog.bat
Note The batch file would be a customization done by CA services or a Services Consultant.