Do you mean IP communicator? From what I have read, Personal Communicator works with CUCM, but I haven't read anything about it working with CUCME (UC520 runs a version of CUCME). It also suggests that you need CTI integration as well for it to work. Are you sure you are trying to get Personal Communicator to work and not IP Communicator?
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...