Especially for the development of web service applications, sometimes it is very helpful to see the actual SOAP messages that are exchanged between the client and the server. A handy tool to achieve this is the TCP Monitor tcpmon. First of all, here is the link to the Webstart version: TCP Monitor (Webstart).
The website for TCP Monitor can be found here: https://tcpmon.dev.java.net/
Tcpmon works as a proxy that connects between your client and the server. When you started tcpmon, you have to create a monitor for the server, just input hostname and port of the webservice URL. You also specify a port, where tcpmon is accepting connections on localhost that will be forwarded to the remote web service.
After the monitor is running, you have to change the endpoint configuration of your client. It has to connect to the computer tcpmon is running on (usually localhost) on the port you specified before. Now run your client as usual and voila: tcpmon shows you the SOAP request, as well as the SOAP response from the server.