I have a few SPA504G's with 1 SPA500S sidecar attached. None of the buttons work or light up. I'm not sure it even has power. I don't see any settings on the phone to configure the side car and nothing in the web interface of the phone.
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...