Not sure what JNDI name would be used without ejb-ref set and no jboss.xml file. I guess ejb-name would be used in this case. Look in the JNDI list in the jmx-console to see what name it is bound to and that the bean is deployed correctly.
your ejb-jar.xml seems to be okay.
You also need a jboss.xml file.
It should loook like this:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE jboss PUBLIC "-//JBoss//DTD JBOSS 3.0//EN" "http://www.jboss.org/j2ee/dtd/jboss_3_0.dtd">
Now you have to put your bean, the interfaces and the two xml files in a jar file and copy it to the server/default/deploy directory of jboss.
As pointed out by Peejay u need Jboss.xml in yr xxx.jar file at the same level as ejb-jar.xml.
Aslo If u still have some problems, just check this as well.