Cross Domain Solution is JSONP

If you encounter the cross domain problem then you should use JSONP. It seems JSONP is going to be adopted in .Net 4 (reference: http://bendewey.wordpress.com/2009/11/24/using-jsonp-with-wcf-and-jquery/)

to use JSONP download the classes

JSONPBehavior

JSONPBindingExtension

JSONPEncoderFactory

JSONPBindingElement

from

http://msdn.microsoft.com/en-us/library/cc716898.aspx

and implement the solution as explained in

http://jasonkelly.net/archive/2009/02/24/using-jquery-amp-jsonp-for-cross-domain-ajax-with-wcf-services.aspx

you can download the code demonstrating the entire solution from aliayman.com/download/crossdomainJSONP.zip

Don't use http://dev.mixendo.com/wiki/Mixendo_XHR/ because it is an additional hub and you are exposing your calls to an external third party.

In order to understand WCF Behaviors and how to create a behavior check the following links

http://benders-blog.blogspot.com/2008/02/making-wcf-part-one.html

http://benders-blog.blogspot.com/2008/02/making-wcf-part-two.html

http://www.jamescbender.com/bendersblog/archive/2008/03/01/making-wcf-quotbehavequot---part-three.aspx

http://wcfsecurityguide.codeplex.com/wikipage?title=How%20To%20-%20Perform%20Message%20Validation%20with%20Schemas%20in%20WCF&referringTitle=Home