Using a GWT wrapper on top of the excellent http://jmesnil.net/stomp-websocket/doc/ Jeff Mesnil's Stomp javascript library we can create a pure java JMS client for GWT.
No need for polling or comet style messages, all you need is to listen to the correct channel.
In the post, the author shows some code samples, and also discuss the benefits and flaws of this approach. It is just a proof of concept that may help others.