Did you have any luck in reaching a conclusion. I am currently using JBoss 4.2.1 to make asynchronous web service calls to a .NET webservice. We used Apache CXF 2.2.2 to generate the client side code and are using the callback handler approach. I can make a successful call to the webserivce and recieve a valid response successfully. But if we recieve a Web Service Fault from the .NET service it fall through the cracks and is not caught by our application code.