If you ever like to show a Modal Progress dialog like the above for any ajax operation no matter which Update Panel or Web Service call is responsible for it, the following code will do the same.
The main trick is hooking the two special events of Sys.Net.WebRequestManager class. This class is responsible for managing all kinds of communication with the server, even a manual invoke of a Sys.Net.WebRequest class will bring this class into action. It fires the invokingRequest before making an Ajax call and fires the completeRequest once the method completes. We are simply showing/hiding the modal popup extender in these events.