gistfile1.cs

[ServiceContract]
public class ContactsResource
{
    private static int nextId = 1;

    [WebInvoke(UriTemplate = "", Method = "POST")]
    public JsonValue Post(JsonValue contact)
    {
        var postedContact = (dynamic)contact;
        var contactResponse = (dynamic)new JsonObject();
        contactResponse.Name = postedContact.Name;
        contactResponse.ContactId = nextId++;
        return contactResponse;
    }
}