In The Castle, any phone call from the town to the castle causes all telephones in the castle to ring. Anyone can pick up. I thought this was the origin of the name but I’m probably wrong.
The castle is full of administrative offices and various bureaucratic departments that run the town.
The protagonist gets the number of a bureaucrat and wants to contact him at his office in the castle.
The fact that the number he’s given causes all phones in all offices in the castle to ring, and the people who answer don’t know or care about what he’s after, just adds a layer of confusion and difficulty to his goal of getting to the castle.
