Johannes joined a Bioclipse Workshop a long time ago, and introduced the participants to the idea of using XMPP (aka Jabber) for asynchronous web services. SOAP is commonly user to run webservices over HTTP, but via (SMTP) email and XMPP is possible too (see SOAP over XMPP). Using HTTP as transport layer has problems. The biggest problem, is possibly that HTTP connections are timed out, e.g. by intermediate router.