I read a few articles about logging your outgoing and incoming SOAP messages. The simpliest way I found to trace SOAP messages is here-
Rick Stahl's Blog - http://www.west-wind.com/weblog/posts/205198.aspx
More Info from MS - http://msdn.microsoft.com/en-us/library/ms730064.aspx
Another useful tool called Web Services Studio Jason from the Arizona .Net User Group pointed me too-
- is also very useful for debugging older web services (though it works with a lot of WCF stuff too).