The ASP.NET Framework does provide support for accessing a Web service asynchronously. The user can wait until the request completes, can block on the WaitHandle, or wait for a callback function to be invoked. However, WSE 2.0 provides a potentially more powerful way of communicating with a Web service by using WS Addressing.
WSE 2.0 is a .NET component that can be downloaded and installed into the .NET Framework. WSE is a Soap Extension that manipulates SOAP messages on both the client side and the server side if implemented in both. It provides a way to communicate by using industry standard SOAP messages, which in turn allows for interaction with Services implemented in other technologies. WSE v2.0 has some classes that allow standardized SOAP messages to be sent based on WS-Addressing, WS-Messaging, and the rest of WS-* specifications.
http://www.codeguru.com/Csharp/Csharp/cs_webservices/tutorials/article.php/c10669/