See
this thread for an answer to your first question.
As to your second, there are no definitive answers. 240/120 is commonly used in residences, 208/120 in light commercial, and 480/277 heavy commercial to industrial, tho you may find a 480V system at a retirement community and a 208V system in an industrial plant, or find both systems together.
If you mean equipment, it varies also. Much of the eqpt designed to run on 240V can also run on 208V. Most lighting ballasts can accept 120-277V input. There's really no delineation other than 3ph eqpt is not made for residential use.
