To change any configuration options on a Cisco 7940 or 7960 series voip handset itself (not over tftp), you need to enter in a unlock config password. This may be needed if you want to set up the handset with a static IP address.
To get to the unlock config screen, press the “Settings” button, scroll down to “Unlock Config”, and press the “Select” softkey. You will now be asked to enter the password.
The default password is “cisco”.
As you need to enter this password via the numeric pad, it should be entered as 222444777722266. Make sure its cycling through the letters on the screen, and not actually entering the numbers as the password.
The menu will go back to the “Settings” screen, and the menu option should have changed to “Lock Config”.
This may also apply to other Cisco VOIP handset models.