“A Visual Studio add-in that allows you to graphically design .NET Configuration Sections and automatically generates all the required code and a schema definition (XSD) for them.”
Here is a sample project which will show you how to send and receive JSON data from a WCF service using three of the most popular javascript libraries. You can do it without the libraries but why reinvent the wheel. Also, this is actually a VS2008 Studio Template so just download and drop the file into My Documents\Visual Studio 2008\Templates\ProjectTemplates\Visual C#\ and enjoy.
To use the template, goto File\New Project\Visual C# and look to “My Templates” and you should see WCF JSON.