Yealink supports having different ringtones to differentiate between internal and external incoming calls. However, they require that this feature also be supported by the VoIP service, which is not ...
How I get around this is I will create a line key and program that line key on anyone who needs to receive those calls as a button on their phone. I then create a dial plan for that number to point to that ext number. Then on the Yealink phone I can set the ring tone for the line to what I want it to be. I can do a GoToMeeting if you would like to see how I do it. Let me know.
Thank you,
Michael Adams