Telecommunication goes back a lot further than you might expect. While the word has become synonymous with television broadcasting and phone communication, it really describes any communication system over a distance, and could include smoke signals. These simple signals were used to convey messages from "the enemy is approaching" to the fact that a whale has beached itself and can be butchered for meat.
While some ancient cultures varied smoke colors to convey further information, there's only so much you can get across with a big fire. One particularly cool ancient version of telecommunication, which aimed to convey more precise meanings, was the hydraulic telegraph, used in Ancient Greece in around 350 BCE.
The idea – thought to have been invented by Aeneas of Stymphalus, a writer on the military at the time – was simple, but neat. Each person you want to communicate with is given a jar of the same size, filled with the same amount of water. Inside the jar is a floating rod, on which was inscribed identical messages that are useful to pass along.
"In each section should be written the most evident and ordinary events that occur in war, e.g., on the first, 'Cavalry arrived in the country,' on the second 'Heavy infantry,' on the third 'Light-armed infantry,' next 'Infantry and cavalry,' next 'Ships,' next 'Corn,' and so on until we have entered in all the sections the chief contingencies of which, at the present time, there is a reasonable probability in wartime," a translation of a contemporary account by Polybius reads.
When someone wanted to send a message, they would signal to the receiver using a fire. Then at the same time, the two would pull out a spigot and allow water to drain out of the jar into the basin below (waste not, want not and all that). The result was that the water level should be at the same height for both participants, with the rod floating to display the same inscribed message.
Centuries later in Britain, civil engineer Francis Whishaw invented another, more complex, system for communicating information at a distance using water. This system linked two devices via pipes, and used changes in pressure to alter water levels in the receiving device, again conveying information via water levels. Despite successful demonstrations, the idea did not take off.