Check the Wiki for an example of how to do this.
From what I understand EJB3.0 will not support being exposed as statless bean.
The solution in the Wiki is to wrap your EJB3.0 with an EJB2.1 or POJO and expose that one as a web service.
I think it's scheduled for JBoss 5.
I think we may get it into JBoss 4 too. It already works in CVS HEAD btw.