Seven-digit dialing

7-digit dialing7-digit diallingseven-digit diallingfixed-length seven-digit numberseven digitseven-digit
Seven-digit dialing is a telephone dialing procedure customary in the territories of the North American Numbering Plan, for dialing telephone numbers in the local calling area.wikipedia
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North American Numbering Plan

Area codeArea codesArea code(s)
Seven-digit dialing is a telephone dialing procedure customary in the territories of the North American Numbering Plan, for dialing telephone numbers in the local calling area.
The intent was for subscribers not to have to dial an area code when making a local call or a call within their plan area, resulting in seven-digit dialing.

Central office code protection

exchange code protectioncode protection
Central office code protection made it possible in some low density areas to use seven digits to reach areas in another area code.
Its primary purpose was initially to preserve seven-digit dialing of local calls across a common area code boundary in border communities.

PEnnsylvania 6-5000

telephone number
A few of the largest cities, such as New York, used seven dial pulls ("PENnsylvania 5000" became PEN-5000 and later PEnnsylvania 6-5000, dialled PE6-5000 or 736-5000).
When seven-digit telephone numbers were first assigned in New York in 1920, the three-letter four-number (3L-4N) system had represented the number in the format PENnsylvania 5000.

Ten-digit dialing

10-digit dialingten-digit diallingten digits
Area code overlay plans introduced a requirement in most areas that calls must include the area code, resulting in a 10-digit dialing requirement.
After the implementation of the North American Numbering Plan, placing a local call within the caller's area code involved only seven-digit dialing.

Area code 202

202Area codes in Washington, D.C.
Washington, D.C. (area code 202) to adjacent areas of Maryland (area code 301) and Virginia (area code 703), discontinued on October 1, 1990 to allow assignment of a code in all three area codes.
Washington is thus one of the largest cities where seven-digit dialing is still possible.

Linked numbering scheme

linked-number area
Linked numbering scheme
A local call in this scheme, standardised for the 1951 introduction of direct-dial long distance calling, was originally dialled as a fixed-length seven-digit number and did not require an area code.

Area code 506

506
Besides 506 & 709, 807 & 867 are the other Canadian area codes to still use 7-digit dialling and have yet to be overlaid.

Area code 867

867+1-867867 area code
It is also one of four Canadian area codes yet to be overlaid, the others being 506, 709 (both of which are currently slated for overlays), and 807 for which 7-digit dialling is still used.

Area code 709

709
For now, this and the three other Canadian area codes, 506, 807 and 867 still use 7-digit dialling and have yet to be overlaid.

National conventions for writing telephone numbers

Telephone number formats
Originally, local calls within an area code could be placed by dialing NXX-XXXX, omitting the area code, known as 7-digit dialing.

Area code 807

807
As a result, 807 is the only area code in Ontario without an overlay, and hence the only one still with 7-digit dialling.

Area codes 415 and 628

415/628415area code 415
415 had been one of the few urban area codes that had not been overlaid, making San Francisco one of the largest cities where seven-digit dialing still functioned.

Video modulation

Video signals are usually encoded into binary digit (0, 1) or seven digit pulse-code modulation (PCM), which is a method used to digitally represent original video signal.

Highlands, North Carolina

HighlandsHighlands, NC
It is within area code 828, and all telephone numbers served by the town's exchange begin with 526-, with seven-digit dialing allowed.

Area code 206

206area code
As of January 2017, this numbering plan area was one of the last urbanized areas in the North American Numbering Plan without a code overlay, meaning telephone calls within Seattle could still be originated by seven-digit dialing.

Area code 246

+1 246246+1246
When placing a phone call from Barbados, also known as HPNA, callers simply use seven-digit dialling (i.e. dialling the last seven digits of the phone number).

Area code 868

868(868)+1 868
When placing a phone call from Trinidad and Tobago, also known as HNPA (home numbering plan area) dialling, callers simply use seven-digit dialling (i.e. dialling the last seven digits of the phone number).

Area code 907

907Area codes in Alaska
Local calls and cellphone calls for long-distance service within Alaska, only require seven-digit dialing.

Area code 404

404Atlanta calling area
When 770 was split, these numbers continued to work as both 404-741-xxxx and as 770-741-xxxx, so that only seven-digit dialing was necessary.

Permissive dialing

permissive dialling
Under an overlay plan, permissive dialing refers to the ability to continue to connect calls via 7-digit dialing while also making 10-digit dialing valid.

List of Washington area codes

Telephone area codes in Washington
Before that time, local calls within an NPA could use 7-digit dialing.

Area code 564

564
On 29 July 2017, ten-digit dialing became mandatory for all local calls in Western Washington, replacing the use of seven-digit dialing.

Area code 603

603Area codes in New Hampshire
Since New Hampshire has only one area code, callers in the state can reach any other telephone within the 603 area code with 7-digit dialing.

Telephone number

phone numbertelephone numbersphone numbers
Seven-digit dialing is a telephone dialing procedure customary in the territories of the North American Numbering Plan, for dialing telephone numbers in the local calling area.