How to Reserve an Extension Number Last updated Save as PDF Share Share Tweet Share Loading...NOTICE: 8x8 Click2Pop End-of-Life on 9/10/208x8 & COVID-19: Protecting Our Business and YoursCisco phones to reboot following firmware upgrade on 9/18/20PrevNext 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.