Yes, it's certainly possible. EJB3 supports home interfaces so they can gradually replace EJB2.1 beans and continue to interact with EJB2.x style beans. Take a look at the EJB3 reference21_30 tutorial that is distributed with EJB3.
Thank you for your reply. Which EJB3 distribution are you referring to precisely? Sun's one (GlassFish) or JBoss? Also my question was related to eventually a passage to JBoss 5. Does this version of JBoss support both EJB3 and EJB 2.1?