I'm not sure what you mean by "inbound and outbound" SOAP calls. Are you talking about a request/response scenario?
In either case, what you're looking for is called "exposing an orchestration as a web service" (searching for that will give you better results), which is done using the BizTalk Web Services Publishing Wizard that you'll find in the Visual Studio Tools menu.
Since it sounds like you're doing synchronous messaging, you'll probably want to read the low-latency tuning whitepaper (it was written for 2004, but it still applies in 2006).