How to add cross domain support to WCF service

I’m trying to allow POST requests from my javascript app hosted at localhost:80 to a WCF REStful service hosted at a different port, but somehow it doesn’t work. I’ve tried adding custom properties to the header, as well as adding it programatically in my service’s JSONData method but I’m still getting ‘405 Method not allowed’ in my response. What is the proper approach here ?

Send XML String as Response

I am getting my Request from a third party application(different domain) to my ASP application. I am handling the request and doing the business part in my application and as a acknowledgement I need to send XML string as Response to the same Page which POSTED the request to my Application. I was successful in retrieving the input from Request using the following code