This function is not supported on this platform. However, the UC5xx series is capable of doing this. The only modification you can do to the ringtone is change it for all calls. I know it seems like a few lines of code would solve the problem, but this platform does not do that. The reason for this is the phones do not know how to tell between internal or external calls. The phones use sip and in the invite it just has the invited extension with the from field in the same format, effectively all calls are internal calls because the SPA400/SPA9000 is actually making the call to 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...