“I would be happier if we called them “phone digits” instead of “phone numbers,” because, I repeat, I don’t think they are numbers. If you’re ever not sure if something is a number or not, my test is to imagine asking someone for half of it. If you asked for half the height of someone 180 centimeters tall, they would say 90 centimeters. Height is a number. Ask for half of someone’s phone number, and they will give you the first half of the digits. If the response is not to divide it but rather to split it, it’s not a number.”