Change extension number (CP version 12+ and 2010+)

You can't modify an existing extension, but you can add a new extension to an existing user, then delete their old extension, assuming that you'd like to keep the current user details.*  Despite the hugely long number of steps it takes to describe this, this doesn't actually take long to do - it's just roundabout:

*-Another approach is to simply delete the old user and create a new user with the desired extension.

1. Go to the Users/Extensions: view users page.

2. Click on the user.

3. Open up the orange titlebar with white text labeled "extension settings".

4. Change the location to "home office" or something else.

5. Note down the last four characters of the phone device MAC address.

6. Set the phone device to "virtual device".

7. Also click "add extension" (the link *above* the button).

8. Fill in the extension number you'd like for that.

9. Set the location to "main office" or whatever you'd like. (sorry, location names cannot be changed)

10. Leave the new extension on "virtual device", for the time being.

11. Apply changes.

12. Click on the user again.

13. Open up the user's voicemail settings, and set their voicemail box to "new mailbox".

14. On the orange title bar for the *NEW* extension, click "primary" on the right.

15. Open up the orange titlebar with white text labeled "extension settings" for the new extension.

16. Set the phone device (for the new extension) to the now-available Polycom with the appropriate MAC address.  Be careful not to select a phone device that already has an extension.

17. Apply changes.

18. From the list of users, click the plus sign to the left of the particular user.

19. Delete the old extension number.