The Cisco Unified IP Phone 7931 includes 24 buttons that can be assigned to lines and call features. A 3-color LED provides call status information for each line.

The line buttons are numbered 24-1 from top to bottom. The numbers do not appear on the phone.

There are two ways how the top four buttons can be programmed.

enable
configure terminal
ephone template 15
button-layout set phone-type [1 | 2]**
exit

ephone 3
ephone-template 15
end

** Specifies which fixed set of feature buttons appears on a Cisco Unified IP Phone 7931G that uses a template in which this is configured.

•1—Includes two predefined feature buttons: button 24 is Menu and button 23 is Headset.

•2—Includes four predefined feature buttons: button 24 is Menu; button 23 is Headset; button 22 is Directories; and button 21 is Messages

More on 7931 and CME here.