In the September MSDN Magazine Aaron Skonnard provides an excellent explanation of TCP messaging support in WSE 2.0.  He explains the SoapSender/SoapReceiver classes, which provide low-level control over the messaging (you have to manually create a message to send back if you want to support request-response style messaging), as well as the SoapClient/SoapService classes (that provide methods that make it easier to do things like request-response style messaging).