Just deploy to JBoss and it`ll work ;-)
You need an EJB3 container for EntityManager to work.
Unfortunately, for reasons I won't list, I need to deploy to Tomcat. :-(
What I find frustrating is I was able to deploy the Seam examples to Tomcat with no problem. I have been comparing my config files with those from the Booking and DVD examples, and so far I cannot find a difference that would explain my apps error messages.
I know there are 2 directions here: either take a simple example that successfully deploys to Tomcat and grow from that. What I did was use the Seam command line tool to generate an app and to generate the entities from an existing database. I've been working to modify the auto-generated app to deploy on Tomcat. 2 days later, much frustration and no luck... But I'm stubborn, so I'm going to work some more on it. If I find how to get it to work, I'll pass along my lessons learned.
I have the same problem with jboss-seam from head.