For accessing org.hibernate.Session from a EntityManager, the JBossAS4.x docs for EJB3, recommend:

You can get access to the current underlying Hibernate Session by typecasting your reference to EntityManager.

@PersistenceContext EntityManager entityManager;
 public void someMethod();
 {
 org.jboss.ejb3.entity.HibernateSession hs = (HibernateSession)entityManager;
 org.hibernate.Session session = hs.getHibernateSession();
 }

However, in AS5, the cast throws an CCE:

 [java] Exception in thread "main" javax.ejb.EJBException: java.lang.ClassCastException: org.jboss.jpa.tx.TransactionScopedEntityManager
 [java] at org.jboss.ejb3.tx.Ejb3TxPolicy.handleExceptionInOurTx(Ejb3TxPolicy.java:77)
 [java] at org.jboss.aspects.tx.TxPolicy.invokeInOurTx(TxPolicy.java:83)
 [java] at org.jboss.aspects.tx.TxInterceptor$Required.invoke(TxInterceptor.java:190)
 [java] at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
 [java] at org.jboss.aspects.tx.TxPropagationInterceptor.invoke(TxPropagationInterceptor.java:76)
 [java] at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
 [java] at org.jboss.ejb3.tx.NullInterceptor.invoke(NullInterceptor.java:42)
 [java] at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
 [java] at org.jboss.ejb3.security.Ejb3AuthenticationInterceptorv2.invoke(Ejb3AuthenticationInterceptorv2.java:186)
 [java] at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
 [java] at org.jboss.ejb3.ENCPropagationInterceptor.invoke(ENCPropagationInterceptor.java:41)
 [java] at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
 [java] at org.jboss.ejb3.asynchronous.AsynchronousInterceptor.invoke(AsynchronousInterceptor.java:106)
 [java] at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
 [java] at org.jboss.ejb3.BlockContainerShutdownInterceptor.invoke(BlockContainerShutdownInterceptor.java:67)
 [java] at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
 [java] at org.jboss.aspects.currentinvocation.CurrentInvocationInterceptor.invoke(CurrentInvocationInterceptor.java:67)
 [java] at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
 [java] at org.jboss.ejb3.stateless.StatelessContainer.dynamicInvoke(StatelessContainer.java:487)
 [java] at org.jboss.ejb3.session.InvokableContextClassProxyHack._dynamicInvoke(InvokableContextClassProxyHack.java:53)
 [java] at org.jboss.aop.Dispatcher.invoke(Dispatcher.java:91)
 [java] at org.jboss.aspects.remoting.AOPRemotingInvocationHandler.invoke(AOPRemotingInvocationHandler.java:82)
 [java] at org.jboss.remoting.ServerInvoker.invoke(ServerInvoker.java:908)
 [java] at org.jboss.remoting.transport.socket.ServerThread.completeInvocation(ServerThread.java:742)
 [java] at org.jboss.remoting.transport.socket.ServerThread.processInvocation(ServerThread.java:695)
 [java] at org.jboss.remoting.transport.socket.ServerThread.dorun(ServerThread.java:522)
 [java] at org.jboss.remoting.transport.socket.ServerThread.run(ServerThread.java:230)
 [java] Caused by: java.lang.ClassCastException: org.jboss.jpa.tx.TransactionScopedEntityManager
 [java] at org.jboss.tutorial.hibernate.bean.AnotherCustomerBean.getCustomer(AnotherCustomerBean.java:68)

for this line:

org.jboss.ejb3.entity.HibernateSession hs = (HibernateSession)entityManager;

From the javadocs of javax.persistence.EntityManager, i see that there is a getDelegate method available which can be used instead. So i have changed the reference doc and also added a new tutorial with this piece of code, which is working;

public Customer getCustomer(long id)
 {
 org.hibernate.Session session = (Session) em.getDelegate();
 return (Customer) session.get(Customer.class, id);
 }