Phone calls also assume the person on the other end wants to be bothered. If you choose to not answer, you’re treated like the a-hole and are expected to explain why (“I’ve been trying to call you. Why haven’t you picked up?”)

To quote Stephen Fry:

“A telephone is a fantastically rude thing. I mean, it’s like going ‘speak to me now! Speak to me now! Speak to me now!’. If you went to someone’s office and banged on their desk and said, ‘I will make a noise until you speak to me’ it would be considered unbelievably rude.”