Just happened to me last week. Unfortunately the only fix I was able to find was doing a factory reset and starting over. I usually save my configurations to a USB drive before I do any firmware upgrades so I can easily reload, and that came in handy.
The interesting thing was that after I did the factory reset, my firmware was upgraded, so it did indeed work. Sometimes the equipment will get mad and wont let you reset it unless you leave it unplugged for a few minutes.
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...