**Answer for 6.4.1 or younger**
By default the request and response SOAP-ENVELOPE is logged to the runtimeLogger with the category web_service_process.
![alt text][1]
You may need to adjust your log4jconfig.xml so that the logs are collected in an extra log file: http://developer.axonivy.com/doc/latest/EngineGuideHtml/monitoring.html#d5e4421
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**Answer for 6.0 until 6.4**
This is possible by registering a LogginIn/Out Intercepter for the webservice technology that we use (CXF). See http://stackoverflow.com/questions/8065737/how-to-log-apache-cxf-soap-request-and-soap-response-using-log4j
Unfortunately it seems like Designer users have no access to get into the relevant code parts to register custom interceptors. But I think that would be cool improvement for the future...
For now I can provide you a patch where these logging interceptors are in use. Just tell me the ivy version where you need it and whether you need it for a designer or an engine.engine.
[1]: http://answers.axonivy.com/upfiles/wsProcessSoapEnvelopeLog.PNG