The ability to set aliases on a user/extension. For example say my user is extension 200 having an alias section where I could add norlem and 250 etc. This can be an extremely clean and useful tool for call routing. Also separating phone provisioning from the user/extension is something that has been really helpful in systems that integrate configuration provisioning like yours does! This provides a clean way to assign private line keys from several extensions which can be an extremely valuable tool during deployment. For example someone may want line one to be their extension for company A and line two to be their extension for company B in the same office. Or the second line could be a sales line etc. It provides a very easy way for the caller to know who the caller is trying to reach by glancing at the phone to see which line key is blinking. It also makes the common scenario of a user registering to more than one phone extremely easy and clean.