A message-driven bean instance has no state for a specific client. However, the instance variables of the message-driven bean instance can contain state across the handling of client messages. Examples of such state include an open database connection and an object reference to an EJB object.
The table with allowed operations in the same specs tells that "Enterprise bean access" is possible from onMessage() only. Do you know how and when to get the reference to a session bean object and keep during the MDB life-time? Thanks, Viktor