Hello rss,
If you want to invoke a web service from a JCD you will have to build the SOAP message using JAX-RPC or AXIS and then programmatically creat an HTTP connection.
Or you can leverage the HTTP(S) eWay and then you only have to build the SOAP message.
Or use eInsight. You can import a WSDL into eInsight and eInsight will offer you a business process Activity to invoke the web service operations defined in the WSDL.