That reminds me of an incident in my first office job many, many years ago. In an open plan office, one of the engineers would listen to his voicemails on speaker at a very loud volume.

Some other wags in the office (I promise you it wasn't me!) rang his extension one night and left a very, very naughty embarrassing and inappropriate message on his voicemail for the whole office to hear the next morning.

It had the intended effect...he never again listened to voicemails on speaker.