What I found out about telegrams:
A telegram is a message that is sent by telegraph, wire, and delivered to people in Morse code.
A person calls the post office and says what they want to say. Then the office sends the message to the person that the caller wanted to speak to. The office writes it in Morse code then sends. And the person on the other end received the message and tries to figure out what it means.
I think that telegrams were used to pass messages around the world.