JBoss Service Requirements
The minimal requirement for a JBoss service is any concrete POJO. Actually the service must be a JMX compliant MBean, but you can create an MBean from any POJO using a ModelMBean implementation such as XMBean or Apache Modeler.
Typically in JBoss, most Services are Standard MBeans. All Standard MBeans can alternatively be deployed using XMBean so this gives the greatest flexibility.