Message driven beans are designed to be usable with other messaging systems, not only JMS.
When connecting to some other system that may send messages to message-driven beans, the Java Connector Architecture may be used to connect the Java EE application server with the other system.
The gizmo enabling other systems to talk, and listen to, the application server is called a resource adapter.
The JMS resource adapter only have one single onMessage method in the interface that a message-driven bean that wants to receive JMS messages need to implement.
Some other resource adapter may have more than one method in the corresponding interface. It is then up to the resource adapter to choose which method to invoke.
This is a slightly theoretical discussion, since I have never seen anything but message-driven beans listening for JMS messages - perhaps someone else has some example in store.