Dan Diephouse just blogged about the announcement of a public review of a JMS SOAP binding and IRI scheme from BEA, IBM, Sonic and Tibco. This is a great news for JMS/SOAP interoperability !
He mentioned that the content-type header has a limited value because of the lack of support for very large messages in JMS. While this may be true for some providers, ActiveMQ provides such a feature.
Also, I'd like to mention I would have been very happy to have a JMS Binding for non-SOAP WSDLs, like the WSDL2 HTTP Binding. I think it would be even more useful !
Anyway, hopefully ServiceMix will have support for the spec soon ...