The Service Classes
There is normally only one service class per app. The service class' job is to get data from the back end and perform some biz logic on it and return it to the front end (actions). There should be one service interface and one class that implements it, e.g. OasSkeletonService, and OasSkeletonServiceImpl.
For SAP apps, the service calls RFCs and converts their proxy data into biz model objects. The service class should be a subclass of SAPServiceSupport which provides methods to call the back end and process errors.
For Hibernate apps, the service calls the daos to get biz objects and performs whatever biz logic is necessary on them.
The service spring beans are configured in applicationContext.xml (not in action-servlet.xml).
As long as the application service extends SAPServiceSupport which is in mortar, it does not have to handle error messages because the superclass handles them.