We can hardly imagine being excited to receive a ball of string in the mail (except, perhaps, for the cats among us), but there was a time when we thought that was the future of correspondence. A device created by a Swiss inventor could record sound patterns on a cellulose thread using a sapphire stylus that could then be listened to using a reproduction machine. When recorded, the thread was small enough to coil up and mail in a standard envelope.
The article says that the machines were implemented in a few business offices, where we imagine the secretaries got rather tangled up.
Read the full story in "Talking Thread" Reproduces Human Voice