We take for granted our sophisticated technology when it comes to communication, making fun of the old geezer with the phonograph and funnel or the paper cups on strings. In the 19th century, wave guides were used in some household to communicate from room to room, with simple signal of whistles to attract attention and then open valves on both ends could allow people to speak to each other.
A very interesting article. Read it in full here:
Can You Hear Me Now? Sound Technology of the 19th Century