Editing Telephone numbering plan (section)

===Variable-length dialing===
Within the North American Numbering Plan (NANP), the administration defines standard and permissive dialing procedures, specifying the number of mandatory digits to be dialed for local calls within a single numbering plan area (NPA), as well as alternate, optional sequences, such as adding the prefix 1 before the telephone number.

Despite the closed numbering plan in the NANP, different dialing procedures exist in many of the territories for local and long-distance telephone calls. This means that to call another number within the same city or area, callers need to dial only a subset of the full telephone number. For example, in the NANP, only the seven-digit number may need to be dialed, but for calls outside the local numbering plan area, the full number including the area code is required. In these situations, [[ITU-T]] Recommendation [[E.123]] suggests to list the area code in parentheses, signifying that in some cases the area code is optional or may not be required.

Internationally, an area code is typically prefixed by a domestic trunk access code (usually 0) when dialing from inside a country, but must not be dialed when calling from other countries; there are exceptions, such as for [[Telephone numbers in Italy#Numbering plan|Italian land lines]].

To call a number in Sydney, [[Australia]], for example:
* xxxx xxxx (within [[Sydney]] and other locations within [[New South Wales]] and the [[Australian Capital Territory]] - no area code required)
* 02 xxxx xxxx (outside [[New South Wales]] and the [[Australian Capital Territory]], but still within Australia - the area code is required)
* 61 2 xxxx xxxx (outside [[Australia]])

Dialing internationally, the country code must be preceded by the [[international access code]], which is ''00'' in many countries per ITU recommendation. This is indicated in notation when the character ''+'' precedes the area code. Some telephone types, especially mobile phones, allow the + to be entered directly, causing automatic substitution by device or the carrier. In the North American Numbering Plan, the prefix is ''011'' before the destination country code.<ref>{{Cite web | url=https://www.fcc.gov/consumers/guides/international-long-distance-calling-made-simple-tip-sheet |title = International Calling Tip Sheet|date=2011-07-19 |website=fcc.gov}}</ref>

[[New Zealand]] requires the area code to be dialed when calling between two local calling areas.

In California and New York, because of the existence of both overlay area codes (where an area code must be dialed for every call) and non-overlay area codes (where an area code is dialed only for calls outside the subscriber's home area code), "permissive home area code dialing" of 1 + the area code within the same area code, even if no area code is required, has been permitted since the mid-2000s. The manner in which a call is dialed does not affect the billing of the call.  This "permissive home area code dialing" helps maintain uniformity and eliminates confusion given the different types of area code relief that has made California the nation's most "area code" intensive state.