Since the phone is unlocked your research turns to what sort of cellular radio is in that phone. You'll find the most common is GSM and then you get to figure out what bands it support. Read http://en.wikipedia.org/wiki/GSM
Now that you have that figured out then you head to your Brazilian cellular carrier and see if they have GSM and what bands they work.
This is not something the maker of the phone can assure you. They might write it may work but moving a phone around the world is not a sure thing.