Area code 664 is a telephone area code in the North American Numbering Plan (NANP) for Montserrat, a British Overseas Territory in the Caribbean. The digits of the area code translate to MNI in the alphanumeric mapping on telephone dials. The area code was created in a split of area code 809, which had been assigned in the 1960s to all of the Caribbean islands. All existing central office codes and telephone numbers were carried from area code 809 to 664, as established. A permissive dialing period was conducted from 1 July 1996 to 1 June 1997 during which use of either area code was permitted for calls into the country terminating in previously established central offices. Destinations with newly issued central office codes required the new area code.