Ang Cui and Michael Costello give a talk at the 29th Chaos Communications Congress in Hamburg titled, Hacking Cisco Phones.
Just because you are paranoid doesn’t mean your phone isn’t listening to everything you say
The two speakers “demonstrate practical covert surveillance using constant, stealthy exfiltration of microphone data via a number of covert channels.” Introspectively there are social issues around convincing people that phones matter.