Ah yes, the good old Trimphone! We had a couple of those back in the early 1970s.
A little known feature was that the microphone wasn't at the end of the handset, there was a transducer somewhere in the middle of the handset connected by a stethoscope-type tube to the speaking end. So if someone put their hand over the 'microphone' to prevent you hearing what they were saying to a third party, you could in fact still hear every word!
Last edited by BEagle; 20th May 2012 at 19:29.