You must be aware of  Outbound Communications Manager (OCM) business service which is mainly used for sending emails from Siebel Application.This is a out-of-box business service, which provides method like SendMessage or SendSmtpMessage , CreateRequest, SubmitRequest methods for sending email from Siebel Workflow Processes or Custom Business Services. But there is a very UNIQUE use of Outbound Communications Manager which provides two specialized methods which are HIDDEN and not visible in Siebel Tools -> Business Service object. These methods are ‘ExpandedText’ and ‘ExpandedSubject’.

Also you should also know what is Communications Template …