http://weblogs.asp.net/paulomorgado/archive/2008/12/15/how-to-issue-server-callbacks.aspxCallbacks were introduced in ASP.NET 2.0 and is a simple mechanism for calling page or control functionality without page rendering and without the user noticing a post back. For a page or control to handle callbacks, all it needs is to implement theenCommunityServer 2007 SP1 (Build: 20510.895)