Mike, I've been involved in a number of interoperability tests with many vendors. See http://www.xmlbus.com/interop/overview/welcome.htm for an overview.
You may or may not find the following useful, but what I have found is that by and large all of the SOAP implementations generate valid and SOAP 1.1 compliant messages. Furthermore, each consumes nearly every message that THEY can produce. However, due in a large part to all of the variability permitted in the SOAP specifications, I have yet to find ANY implementation which accepts EVERY valid SOAP message that can be produced. What I will say is that: (1) Apache Axis is able to correctly consume a significantly larger number of valid messages than Apache SOAP. (2) interoperabiliy of SOAP implementations compares favorably to virtually any other protocol, particularly if you pick up a fairly current implementation from your vendor. More information on the relevance of namespaces and interoperability can be found here: http://radio.weblogs.com/0101679/stories/2002/01/25/whatObjectDoesSoapAccess.html http://radio.weblogs.com/0101679/stories/2002/02/01/toInfinityAndBeyondTheQuestForSoapInteroperability.html - Sam Ruby
