To answer the question, a bean instance is MAY NOT be the same for all clients of a stateless session bean. You never know whether you are calling method on the same bean instance you were talking to. The container might have got a new instance from the pool to serve your next request.
Consider this scenario:
1. Container has 3 bean instances in a pool, A, B and C.
2. Client 1 makes a method invocation, which is served by A.
3. Client 2 makes a method invocation, which is served by B.
4. Meanwhile container might moved A back to pool.
5. Next time client 1 makes a method invocation, container may choose C to serve this request.
Having a pool of bean instances can facilitate multiple clients calling methods on
EJB at the same time. Cocunrrency is different issue.
Hope it helps.
Regards,
Nandu