"Oi" is a British version of "Hey", also a music style.
In
Portuguese, Oi means "Hi". Maybe Britain get the accent of the
Portuguese while they saved them for the Spanish king.
Oi is used(used to call someone, or to say "hi" in other version) in Australia,America,Canada, and, duh,
Portuguese countries.
Many people in North America(Yep, Mexico and Greenland count) says "oi" as a natural part of their language or to do the same thing we do.