Calling Puerto Rico from the United States explained:
1 - North American long distance prefix
787/939 - area codes assigned to Puerto Rico (the two codes overlay, both serving the entire area)
local phone number - 7 digits
US to Puerto Rico international dialing format:
1 787 ??? ???? or 1 939 ??? ????
this US territory is in the North American Numbering
Plan (calling it works like a US long distance call)...however,
international or sometimes unexpected charges may apply when calling numbers in area codes 787 or 939!