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However, in parts of North America, especially where a new area code overlays an older area code, dialing 1 + area code is now required even for local calls, which means that the NANP is now closed in certain areas and open in others. Dialing from mobile phones is different in that the trunk code is not necessary. Open and closed dialing plan should not be confused with open and closed numbering plans. A closed numbering plan, such as found in North America, features fixed length area codes and local numbers. An open numbering plan, as found in assorted countries that have not yet standardized, features variance in length of area code or local number, or both. Closed dialing plans are rare where numbering plans are open.
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