Maybe the term "PO box" isn't accurate, my mistake. But the fact is that it's a system that establishes a physical adress in USA for my name so I can buy in american sites that do not deliver worldwide. Very useful , plus they manage everything , taxes etc.and I get my stuff delivered at my door.
I know it works from the SB e-store because I bought the tunes some weeks ago and it is already waiting for the Rio Car to arrive (I can manage sending schedules, etc). Everyone in Latin America who buys things in Amazon and other places alike has mail boxes, normally in Miami.