Follow these instructions to factory reset your Cisco phone:
- Remove the ethernet (network) cable.
- Wait one minute.
- Replace the ethernet cable.
- Press and hold the # key within ten seconds.
- The Message Waiting Light will start to flash. Release the # key.
- Press the following keys in sequence: 123456789*0#
- Wait for about twenty minutes for the reset to complete.
Watch the video below for visual instructions.