The North American Numbering Plan is a unified telephone system used by the USA, Canada and some Caribbean nations. Dialing between these countries does not require using international codes. In other words, a call between New York and Los Angeles has the same dialing format as a call from New York to Jamaica.
In the case of regular telephone numbers, rates are generally low. However, some scammers will try to make you call Pay Per Call numbers and, in this case, much higher charges may apply. This practice isn't even illegal because calling foreign numbers evades US jurisdiction, so whatever rules the USA has in place for Pay Per Call services do not apply when dialing these numbers.
The practice's name is '809 scam' because, for many years, 809 was the single area code used by several Caribbean islands. In the meantime, many other codes have been activated and 809 currently serves the Dominican Republic.
If you live in the USA or Canada and you want to dial a telephone number starting with an area code you do not recognize make sure you first check to see whether the area code belongs to another country using the North American Numbering Plan. Here's a list of all NANP countries and their area codes.