Extension Routing allows you to easily and visually control which extensions are allowed to use specific outbound routes.
Normally, to block extensions from using an outbound route, you either have to create a custom context for each extension you want to modify, or do the tedious work of creating custom dial plans. This method is slow. It is NOT easily replicated or checked for errors and omissions. It is not easily configured by novice users.
Want to set up a public area phone that can dial local or internal numbers, but block it from making costly long distance or international calls? Want to completely block employees from your international routes if they don't need international calling? You can do this with the Extension Routing module.
If you have the Class of Service (CoS) module installed and enabled, you will need to use that module to manage route access.