It's late... I've read too much on asynchronous reliable messaging with SOAP. So, here is where I've landed:
1. People are going to use HTTP for everything on the outside of the firewall
2. You can break 1 synchronous call into 2 asynchronous call as long as you have a message correlator.
3. It looks like WS-Routing will provide wire syntax for correlation - thank you MS for an early impl, too.