You didn't mention which framework u are using for web services.
Anyway, as fars as i'm aware in terms EJB beans only stateless session beans can be used as an end point.
But if u need to invoke methods on BMP /CMP enity bean then use stateless session bean as a session facade and invoke operations on yr desired entity bean.
Have a look th this .
I hope this helps.
But do write back if you get any other information on that.