This new feature added to the 7.4.7 firmware release seems to be a really great improvement...but there's no supporting documentation. I've tried using the RFC outlined CANCEL message with the "Reason" header, and the phone returns a 200 OK message. However, no changes appear on the phone.
What would be great is an option to cancel the "missed call" alert on any phone that receives this message. This would be especially useful on ring/hunt groups, where multiple phones ring and only one picks up. The Reason: SIP;cause=200;text="Call completed elsewhere" message would be sent to the other phones in the group, and the missed call alert would be removed (or altered to be shown as a 'Received call').
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