To reboot Cisco 7940/7960 IP phone hold down the following keys :-
"*" and "6" and "Settings"
To reboot a Cisco 7941 Series: Push the settings button and while on the Settings screen push **#** and after a few seconds the phone will start to reboot.
To reboot a Cisco 7941 Series: Push the settings button and while on the Settings screen push **#** and after a few seconds the phone will start to reboot.