Both the older Cisco SPA range and the new CP range support distinctive ringing through the use of Alert-Info SIP headers.
The names to use can be found in the web interface for both phone types. In the web interface, the settings are in the Voice section, phone tab, Ringtone heading.
On CP phones:
On SPA phones:
The important part for Alert-Info is the name part after “n=”. The Alert-Info header must look like these examples:
So simply put the name of the ringtone in the header and nothing else. This is different to most phones (and actually not as specified in the SIP RFC) as they need to have a dummy URI inside them.
As an example, if you wanted to add this header in Asterisk, use the SIPAddHeader application: