To Factory Reset a Cisco IP Phone do the following:
1. Press and hold #, disconnect and reconnect Power
2. The Phone will check through the Line LEDs, on an 7911 or similar it will just light up the both Menu Keys and the Reciever \ Handset LED - after that, let go of #
3. Enter following: 1 2 3 4 5 6 7 8 9 * 0 #
4. The Phone should start up and grab the latest config from your Callmanager

To just Reboot a Cisco IP Phone do following:
1. Go into any Menu
2. Enter #
3. Phone does reload
( 7940, 7960: Hold *,6,Settings )

To open up the Configuration on a Phone:
1. Go into Menu Setting
2. Enter **##

To Factory Reset and erase the firmware on a Cisco IP Phone do the following:
1. Press and hold #, disconnect and reconnect Power
2. The Phone will check through the Line LEDs, on an 7911 or similar it will just light up the both Menu Keys and the Reciever \ Handset LED - after that, let go of #
3. Enter following: 3 4 9 1 6 7 2 8 5 0 * #
4. The Phone should start up and grab the latest Firmware from your Callmanager