The Cisco SPA500DS LCD screen backlight is not separately controlled. If the IP phone backlight is on, the Cisco SPA500DS backlight is on. If the IP phone backlight is off, the Cisco SPA500DS backlight is off. The Back Light Timer parameter is configured in the management interface in the User tab, in the LCD section.
It should work for firmware 7.5.2b and newer or you have come across a firmware bug.
Configure Multicast Paging on the Cisco IP Phone 7800 Series or 8800 Series Multiplatform Phone
The Cisco IP Phone 7800 and 8800 Series Multiplatform Phones provide voice communication over an Internet Protocol (IP) network...
Add Call Park on a Cisco 7800 or 8800 Series Multiplatform Phone Key Expansion Module
Call park allows the user of the phone to put an incoming call on hold so that the call can be retrieved on another phone. A call is park...