All apartment telephone lines will use wifi? for the telephone line. With the difference between the home and personal numbers, the home number is tied to the unit whereas the personal number is tied to the person. If I had foster children, they might have a personal smartphone that is for them. However, when someone calls the penthouse from the public foyer, the penthouse’s number will ring. When a pizza delivery is made, they will call the penthouse phone number. As you can see, the number is tied to the penthouse. If everyone called the pizza shoppe from their personal line, they may have to identify the apartment number. Regularly calling from the penthouse’s phone line, the pizza shoppe will be able to recognize that to be for the penthouse.