How to Reserve an Extension Number Last updated Save as PDF Share Share Tweet Share Loading...Can't log in to VOD? Old versions have been retired...Looking for user guides and product manuals? Click here!PrevNext Objective To reserve an extension number in Configuration Manager. Applies To Configuration Manager Extensions Procedure Log into Configuration Manager. Click Extension Numbers. Click Reserve Extension Numbers (top right). Complete the fields, as seen below. Click Save. Best Practice It is best practice that the below extension numbers marked as reserved are not used.