I know this post is a bit old now, but if you happen to be using .NET 4, you should look at using URL Routing (introduced in MVC, but brought into core ASP.NET).
In your app start (global.asax), just have the following route configuration line to setup the default route:
RouteTable.Routes.Add(new ServiceRoute("mysvc", new WebServiceHostFactory(), typeof(MyServiceClass)));
then your URLs would look like this:
http://servername/mysvc/value/2
HTH
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…