There is an interesting developerWorks article covering the JAX-RPC Web Services support in WebSphere Application Server Version 6.1. It demonstrates how this support alone can provide some of the benefits normally associated with an enterprise service bus, namely location transparency (WSDL endpoints can be overridden in the administrative console) and protocol transparency (SOAP/HTTP, SOAP/JMS or RMI/IIOP). As the article goes on to state, the combination of WebSphere ESB and Service Registry and Repository can give you much more dynamic behaviour when trying to achieve the first of these but if all you need is the ability to modify endpoints when, for example, moving from the development environment in to production, then this may suffice.