I have lived all over the western USA and Hey is NOT used as hello. I am nearly 60 years old and it's news to me that people interchange Hey with hi or hello. No one where I live or work in the Denver, Colorado Metro would use Hey to say Hi. Hey is used to interrupt or get attention, usually preceding a warning.. So Hey puts you on guard and if I hear HEY!, my first reaction is "What?" The feeling inside is the exact opposite of Hi or Hello... it causes tension and alertness to danger.