There is definitely an event triggered that could be tracked, otherwise music on hold would never work.
-- SIP/FlowRoute-b683f810 is making progress passing it to SIP/1184-08269860
-- SIP/FlowRoute-b683f810 answered SIP/1184-08269860
(hold button pressed)
-- Started music on hold, class 'default', on SIP/FlowRoute-b683f810
(call resumed)
-- Stopped music on hold on SIP/FlowRoute-b683f810
Could this not be tracked in QM somehow, since it is one of the more important metrics in determining agent performance in an inbound call center.