With the end of permissive dialing on July 1, 1998, it replaced the previous International Telecommunication Union country code 670, which was later assigned to East Timor.
Although the Northern Mariana Islands (NMI) became a commonwealth in 1978 and the United States assumed sovereignty in 1986, calling from the United States to CNMI remained an international call (011-670-xxx-xxxx).
After the CNMI was added to the North American Numbering Plan, the U.S. Federal Communications Commission (FCC) regulated calls between the U.S. and CNMI as "domestic", causing a reduction in the cost of telephone calls.
This change also made available national toll-free numbers to callers from the CNMI, which became popular with the advent of pre-paid phone cards.
However, since no mobile telephone carriers in the U.S. are present in the CNMI market,[citation needed] cellular calls to the CNMI are not necessarily considered "domestic" or within the definition of "nationwide long distance".