We remember people by multiple signs and signals.
To know someone, it is not only from the person’s apperance, but also many other elements that relate to this very individual. This is what we called, individuality.
Though most of the time someone remembers a person by his/her face, the overall appearance.
However, when you pick up the phone, the voice from the other side let you know instantly who this person is if the caller is one of your friends.