from the United States explained:
1 - North American long distance prefix
664 - area code assigned to Montserrat
local phone number - 7 digits
US to Montserrat international dialing format:
1 664 ??? ????
this country 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 code 664!