With the end of permissive dialing on July 1, 1998, it replaced the previous International Telecommunication Union country code +670, which is now used by East Timor.
After the CNMI was added to the North American Numbering Plan, the U.S. Federal Communications Commission (FCC) regulated calls to and from the CNMI as "domestic", hence dramatically lowering the cost of these telephone calls.
This change also opened up national toll-free numbers to callers from the CNMI, which became very popular with the advent of pre-paid phone cards.
When a person in the islands calls anywhere in the United States or Canada, he or she simply dials 1 and then the area code and phone number.
For callers in the U.S. or Canada calling to the islands, one first dials 1-670, followed by the seven-digit phone number.