sentences:  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.Although the Northern Mariana Islands (NMI) became a commonwealth in 1978 and the United States assumed sovereignty in 1986, calling between the CNMI and the rest of the United States remained an international call (011-670-XXX-XXXX).As international calling rates began to fall in the more competitive destination countries during the 1990s, it became a considerable financial burden for people calling between the U.S. Mainland and the CNMI.