This would be crucial especially if the phone is hardened, not being able to reset or change settings could prevent a phone registering in a new environment or even when migrating from office to office. This applies even if you are trying to migrate the phone to another platform such as Asterisk/FreePBX etc... This guide applies to nearly all of the Cisco IP phones that you would use in CME or CUCM from several years ago including models: 9900, 9971, 8800, 8900, 8845, 8851, 8841........