Hello there

I'm convinced my landline telephone at work is bugged.
Its being used to transmit all room conversations when the phone is on-hook.
I've inspected the phone internally and compared it against many other identical phones. I've also used very sophisticated TSCM equipment to detect the presence of an unauthorised audio transmission. But nothing could be found.

After inspecting about seventy telephones I found that those phones which I suspect to be bugged at work all have the polarity around the ringer correctly fixed. The bugged phones have positive lead (red wire) connected to the positive terminal and negative lead (black wire) connected to the negative terminal. The clean phones have this connection reversed i.e. positive lead to negative terminal and negative lead to positive terminal. The ringer is a piezoelectric transducer.

Here are pics of the circuit:
http://bit.ly/1C1PoQh
http://bit.ly/1I0AYsd
Note the ringer is the black object seen in the pics.

I just recently came across an article describing how piezoelectric transducers can be used to transmit and eavesdrop.
http://www.reddit.com/r/badBIOS/comments/2e3yuv/badbios_transmits_ultrasound_via...

Can the ringer circuit on this telephone together with the piezoelectric transducer ringer be used to transmit room audio via RF?
P.S. I verified that the ringer can act as a microphone by connecting it to an amplifier.