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 for example.
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 if this area code belongs to another country within the North American Numbering Plan. Here's a list of all NANP countries.