I was able to get this to work by following instructions from a post dated May14 2011 on this very subject;
(oddly enough – I found the discussion using a BING search of “cisco uc320 and cisco sg200-08p” – which returned the link for the cisco user support community discussion, but if I try that search on the cisco support page, I didn’t find it….)
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...