recently installed (as part of my demo lab) a 7916 Exp on my 7965G phone. (After having made 2 false starts, not realising in the Cisco world of pointless SKU's, you need to order a footstand and a power supply separately...)
Plugged in exp module.
Plugged in AUX cable.
Plugged in psu (pwr cube 3 - 48V)
(why is it not PoE???)
Opened CCA, went to my extension and configured a 7916 exp module on the phone.
All this time, every light on the 7916 is on (orange) - all 12 keys plus the 2 'level' buttons - and the Cisco logo is on the screen.
Have to wonder, do I have a faulty unit?
As I just cannot see how to enable it anywhere else? (config on phone is locked of course as it is controlled by the UC560)