Good question. You need to have some controlled endpoint otherwise you would have to communicate something to everyone who has installed this application. Could you put some kind of lookup into the application? Perhaps put an XML file on a web server somewhere, and your app looks at that for the address of the web service? One way or another you need to put something somewhere that you can establish and control the information.
Playing a technical devil's advocate: How can you deploy a client app that uses a web service that is not yet deployed?
-Peter
peterlanoie.blog