Both synchronous and asynchronous calls to the WCF service are pretty simple by using the proxies generated by the Visual Studio. When making a synchronous call, the UI thread that issues the call will be blocked until the WCF service sends the results back to the client. When an asynchronous call is made, the UI thread sends the WCF request and forks a worker thread to wait for the response from the WCF service. The UI thread is not blocked and remains responsive to other user interactions. When the response from the WCF service comes back, the "AsyncCallback" "delegate" is executed to process the WCF service response.
taking from
http://www.codeproject.com/KB/WCF/TwoWaysCallWCF.aspxFor my own reference.
