Looks like some of your keyboard questions stopped working while you were writing your question...............
Anyway, it is not difficult to find out on the net, use a suitable structured query in google, and you mind find some answers
http://www.lmgtfy.com/?q=.net+3.5+wcf+Chat+application
Here is one such example (The 1st result:);
http://msdn.microsoft.com/en-us/library/bb690929.aspx