That assumes you are using either HTTP GET or POST for the web service and not SOAP. Plus it is going to require that you place additional code in the web service constructor to capture the posted data. I’ve done it before this way. It works, but it’s not an elegenat solution and probably takes more time do develop as well.
The proper way do it is to add a reference to the webservice in your BizTalk project. From there you can create an orchestration and add a web service port to send the XML and receive the response.
Ben McFarlin
BizTalk Consultant