You can customize the design of a web service's test page with a single line of code in the web.config file. But like most things in ASP.NET it is not that easy if you actually try it! Although you can find instructions on how to specify a custom wsdlHelpGenerator...
Recently I've discovered a fantastic free service provided by Yahoo! which makes it possible to convert any XML data feed into a JSON data feed. http://pipes.yahoo.com/pipes/ It is easy to create a pipe that provides a JSON data feed with a callback function...