This was a nice project – it involves a 15 minute historical conversation from a historic transcript of the first US transcontinental telephone call. The audio was put it onto a QuickSilver™ QS6112 audio unit with built in amplifier. Visitors get to pick up the phone, and just pop into the conversation wherever it is at that point. The hook on which the ear piece hangs just serves to turn the speaker on and off. The audio replay unit just loops the conversation.
Simple, quick to install, and easy to update. The unit is, of course, wirelessly connected to the rest of the system, with the audio on a local SD card plugged into the device. The TeaParty control system can start the conversation from the beginning through a user interface, or run different audio if required, and it could be triggered from a motion detector or any other sensor – but this was a relatively simple case, with the biggest job being to put new cable on the (original) phone.