Change extension number (CP version 4.x)

Technically, you cannot change extension numbers.  But you can assign phones to new extensions.

1. Go to your Web Admin Panel -> extensions -> view extensions.

2. Click on the old extension number for the phone.

3. Look for "Phones / Devices" on the left.

4. Change "Phones / Devices" to "Virtual Extension".

Open

5. Update Extension.  Now you can assign the the phone/device to a different extension.
   OR: you can simply delete the old extension, skipping steps 2-5 above.

6. Click on the new extension number, or add an extension.

7. Under "Phones / Devices", select the available device.
   Important: Never assign an extension to a device that's already assigned to an extension.*

8. Update extension.

9. You will need to reboot the phone for the extension number on the display to reflect the change.  However, this is cosmetic; the changes have already taken effect.

*-Assigning a second extension to a device that already has an extension can cause unexpected behavior, and only one extension will work.  If two extensions get assigned to the same phone device, set both extensions to virtual, update, and then re-assign them.

Safe extension numbers:

• Three or four digit extensions are recommended.  Five digit is OK.

• Avoid beginning an extension with "9...", unless you use a dial-out prefix other than "9".

• Avoid "85..." as the beginning of an extension.
  (voicemail and conference bridges use 8500-8599)

• Avoid "90..." at all times.
  (call parking is 9001-9050)

• Extensions may not begin with a zero.

• Do not mix extension number lengths.
  (mixing 3- and 4-digit extensions can confuse the phones)

Also see the following article.  This is is useful if the phone will not update the extension number on the LCD:
How to: Change Extension Numbers