Area codes 410, 443, and 667

Last updated July 15, 2024

Area codes 410, 443, and 667 are telephone area codes in the North American Numbering Plan (NANP) for the eastern half of the U.S. state of Maryland. The numbering plan area (NPA) includes the Baltimore metropolitan area and the Eastern Shore. The three area codes are overlay codes for one numbering plan area, among which 410 was the initial area code for the NPA, when it was split from area code 301 in 1991. 443 and 667 found assignment primarily in cellular service and for competitive local exchange carriers, such as Comcast and Cavalier Telephone, when introduced, but have since become universal in carrier availability.

History

In 1947, the American Telephone and Telegraph Company (AT&T) published the first configuration of a nationwide telephone numbering plan for Operator Toll Dialing, which designated the state of Maryland as a numbering plan area and assigned area code 301.^[1] Despite the state being home to two large metropolitan areas, Baltimore and the Maryland suburbs of Washington, D.C. (area code 202), the state received only one area code. This made Maryland one of the most-populous states to be served by a single area code. By the late 1980s, the rapid growth of the Baltimore and Washington suburbs, as well as the proliferation of fax machines and pagers placed the numbering resources in the danger of exhaustion of central office prefixes.

The number shortage problem was exacerbated by the use of area code 202 as a de facto overlay for the inner ring of the Washington metro area, even though it was split between three area codes–301, 202, and Northern Virginia's 703. This was accomplished via a system of central office code protection in which no central office code was duplicated in multiple area codes in the region. Each existing central office code was routed with each area code in the region so that each telephone number in the region could be dialed with any of the regional area codes. The consequence was that the full capacity of central office prefixes could not be used for each involved area code.

The office code protection ended in 1990, but it soon became apparent that this would not free up enough prefixes to meet demand. By the fall of 1990, it was apparent that Maryland needed another area code. In November 1990, a plan for a second area code, 410, was announced, that would be assigned to the Baltimore metropolitan area and the Eastern Shore, while western and southern Maryland, including the Washington suburbs, would retain area code 301.^[2] Bell Atlantic (now Verizon), the largest telephone provider in the region, allowed the western part of the state to retain 301 to keep the large number of federal agencies on the Maryland side of the Washington area from having to change telephone numbers. On the other side of the Potomac River, many of the same factors resulted in most of the old 703 territory outside of Northern Virginia split off as area code 540 in 1995. While Maryland would have needed a second area code at some point due to rapid growth in the Washington and Baltimore suburbs, it is very likely that the immediate need for another area code would have been staved off had it been possible to assign more 301 numbers to the Baltimore area before 1990.

Area code 410 officially entered service on October 6, 1991; it was initially implemented in a permissive-dialing phase, with ten-digit dialing for local calls across the new 301/410 boundary. The split largely followed metro lines. However, slivers of Anne Arundel and Carroll counties, as well as much of western Howard County, stayed in 301 even though these counties reckoned as part of the Baltimore area. Conversely, slivers of Frederick County, a Washington exurb, switched to 410.^[3]^{[lower-alpha 1]} Effective November 1, 1991, ten-digit dialing was required when calling a different area code in Maryland.^[4]

Although the split was intended to be a long-term solution, within five years 410 was already close to exhaustion due to the proliferation of cell phones and pagers, particularly in and around Baltimore. To solve this problem, area code 443 was overlaid onto the 410 territory on July 1, 1997. Overlays were a new concept at the time, and had met resistance because of the requirement for ten-digit dialing. However, the alternative would have been a split that would have forced residents of either Baltimore or the Eastern Shore to change their numbers for the second time in a decade.

By 2011, the 410/443 area was once again running out of numbers because of the continued proliferation of cell phones. To spare residents another number change to a new area code, a third overlay code, area code 667, was implemented on March 24, 2012.^[5] This had the effect of assigning 24 million numbers to just over four million people. Based on current projections, a fourth area code will not be required in the region until about 2030.^[6]

Coverage

The counties served by these area codes include:

In the Baltimore metropolitan area:

All of Baltimore and Baltimore, Calvert and Harford counties
Most of Anne Arundel, Carroll and Howard counties^{[lower-alpha 1]}
A small portion of eastern Frederick County ^{[lower-alpha 1]}

All of Maryland's Eastern Shore:

Notes

1 2 3
Four counties were split between area code 301 and 410.
- Anne Arundel County was assigned area code 410, except Laurel exchanges 210, 317, 490, 497, 498, 596, 604, 725, and 778, Marlboro exchange 952, and Fort Meade exchange 677.
- Carroll County was assigned area code 410, except Mount Airy exchange 829 remained area code 301.
- Howard County was assigned area code 410, except Mount Airy exchange 829 and Laurel exchanges 210, 317, 490, 497, 598, 604, 725, and 776 remained area code 301.
- Frederick County remained area code 301, except Union Bridge exchange 775 and New Windsor exchange 635 was assigned 410.^[3]

Related Research Articles

The North American Numbering Plan (NANP) is a telephone numbering plan for twenty-five regions in twenty countries, primarily in North America and the Caribbean. This group is historically known as World Zone 1 and has the telephone country code 1. Some North American countries, most notably Mexico, do not participate with the NANP.

Area codes 314 and 557 are telephone area codes in the North American Numbering Plan (NANP) in the U.S. state of Missouri, serving the city of St. Louis and most of its inner-ring suburbs in neighboring St. Louis County. The numbering plan area is bordered to the west by area code 636, which serves St. Louis' outer suburbs to the west, south, and north. Across the Mississippi River to the east, 314 is adjacent to area code 618, which serves southern Illinois and most of Metro East. Area code 557 was added to the 314 numbering plan area on August 12, 2022, to form an overlay numbering plan.

In telecommunications, an area code overlay complex is a telephone numbering plan that assigns multiple area codes to the same geographic numbering plan area (NPA). Area code overlays are implemented in territories of the North American Numbering Plan (NANP) to mitigate exhaustion of central office codes in growth areas. The method has been in use since 1992, and has been the exclusive method of area code relief since 2007.

Ten-digit dialing is a telephone dialing procedure in the countries and territories that are members of the North American Numbering Plan (NANP). It is the practice of including the area code of a telephone number when dialing to initiate a telephone call. When necessary, the ten-digit number may be prefixed with the trunk code 1, which is referred to as 1+10-digit dialing or national format.

Seven-digit dialing is a telephone dialing procedure customary in some territories of the North American Numbering Plan (NANP) for dialing telephone numbers in the same numbering plan area (NPA). NANP telephone numbers consist of ten digits, of which the leading three are the area code. In seven-digit dialing it is not necessary to dial the area code. The procedure is also sometimes known as local format or network format.

Area code 564 is a telephone overlay area code in the North American Numbering Plan (NANP) for Western Washington state, including metropolitan Seattle. The area code was first proposed in 1999 to relieve telephone number shortages in area code 360, but implementation was delayed until 2017, when it was installed for an overlay complex that comprises only the numbering plan area 360. Neighboring area codes 206, 253, and 425 were slated for expansion of the overlay upon exhaustion of central office codes in each NPA. In 2023, area code 206 was approved for expansion with a guide line for preparation of inclusion of at least nine months. Ten-digit dialing has been mandatory in all of western Washington since July 29, 2017.

Area code 262 is a telephone area code in the North American Numbering Plan for the southeastern part of the U.S. state of Wisconsin. The numbering plan area comprises suburbs that are a part of the Milwaukee and Chicago metropolitan areas. The area code was created on September 25, 1999, in an area code split of area code 414.

Area code 404 is a telephone area code in the North American Numbering Plan (NANP) for Atlanta, Georgia and its closest suburbs. This comprises roughly the area encircled by Interstate 285. It is an enclave area code, surrounded by area code 770, which serves most of Atlanta's suburbs. Both 404 and 770 are overlaid by area codes 678, 470, and 943.

Area codes 514, 438, and 263 are telephone area codes of the North American Numbering Plan (NANP) for Montreal and most of its on-island suburbs, specifically the Island of Montreal and Île Perrot in the Canadian province of Quebec.

Area codes 202 and 771 are telephone area codes in the North American Numbering Plan (NANP) for Washington, D.C.

Area codes 813 and 656 are area codes in the North American Numbering Plan for the U.S. state of Florida in the city of Tampa, Florida, and its surrounding areas, such as Zephyrhills and Oldsmar. In 2022, due to exhaustion of central office prefixes, area code 656 was added to the service area forming an overlay complex.

Area codes 678, 470, and 943 are telephone area codes in the North American Numbering Plan (NANP) for the U.S. State of Georgia in the Atlanta metropolitan area. The area codes are assigned in an overlay plan to a combined numbering plan area (NPA) consisting of 404 and 770.

Area codes 304 and 681 are telephone area codes in the North American Numbering Plan (NANP) for the entirety of the U.S. state of West Virginia. The numbering plan area was established in October 1947 with area code 304, as one of the eighty-six original North American area codes. Area code 681 was added to the same area in an overlay plan that took effect on March 28, 2009.

Area codes 610, 484, and 835 are telephone area codes in the North American Numbering Plan (NANP) for the eastern and southeastern regions of Pennsylvania. The numbering plan area (NPA) includes regions to the west of Philadelphia and the cities Allentown, Bethlehem, and Reading. It includes much of the Delaware Valley, including almost all of Delaware County, most of the Philadelphia Main Line, and all of the Lehigh Valley.

Area codes 301, 240, and 227 are telephone area codes in the North American Numbering Plan (NANP) for the western part of the U.S. state of Maryland. The numbering plan area (NPA) comprises Maryland's portion of the Greater Washington, D.C. metro area, portions of southern Maryland, along with rural western Maryland. This includes the communities of Cumberland, Frederick, Hagerstown, Gaithersburg, Potomac, Germantown, Bethesda, Rockville, Landover, Silver Spring, and Waldorf.

Area codes 513 and 283 are telephone area codes in the North American Numbering Plan (NANP) for the southwest of the U.S. state of Ohio, including Cincinnati and surrounding cities, such as Forest Park, Hamilton, Lebanon, West Chester, Mason, Maineville, Middletown, Milford, Norwood, Oxford, Harrison, Cleves, Miamitown and Trenton.

Area codes 816 and 975 are telephone area codes in the North American Numbering Plan (NANP) for most of the Missouri side of the Kansas City metropolitan area, the St. Joseph area, and all or part of 15 surrounding counties in northwestern Missouri. The numbering plan area originally comprised most of the northern and western two-thirds of the state, bordering with Arkansas, Illinois, Iowa, Kansas, Nebraska, and Oklahoma, but has been reduced to a ribbon bordering Kansas. 816 is one of the original 86 area codes created in 1947. The numbering plan area was converted to an overlay complex with area code 975 in 2023.

Area codes 440 and 436 are telephone area codes in the North American Numbering Plan (NANP) for the U.S. state of Ohio, serving the parts of the Greater Cleveland area, surrounding the city of Cleveland, but not the city and most of its inner suburbs.

Area codes 703 and 571 are telephone area codes in the North American Numbering Plan (NANP) for Northern Virginia, including the independent cities of Alexandria, Fairfax, Falls Church, Manassas, and Manassas Park, as well as all of Arlington and Fairfax counties and parts of Fauquier, Loudoun, and Prince William counties. Area code 703 was created as one of the eighty-six original North American area codes in October 1947, and originally served the entire Commonwealth of Virginia. Area code 571 was created on March 1, 2000, to form an overlay plan with 703.

In the administration of the North American Numbering Plan, central office code protection is a numbering policy for maintaining local seven-digit dialing in communities that extend on both sides of the boundary line between multiple numbering plan areas (NPAs), such as in cross-border towns on state lines. Code protection prevents the use of the same telephone number on both sides by not assigning the same central office code of one NPA in the adjacent NPA.

References

↑ Mabbs, Ralph (Winter 1947–1948). "Nation-Wide Operator Toll Dialing—the Coming Way". Bell Telephone Magazine. 26 (4): 181. Retrieved July 20, 2023.
↑ "New area code coming". The Baltimore Sun. November 21, 1990. p. E6.
1 2 "New area code for eastern Maryland". The Baltimore Sun. November 1, 1991. p. 1A.
↑ "Now Area Codes Count in Md." The Washington Post. November 2, 1992. p. B9.
↑ Fazeli Fard, Maggie (October 12, 2011). "Maryland's new 667 area code goes into effect in 2012". The Washington Post . Retrieved July 23, 2012.
↑ "2022-1 NRUF and NPA Exhaust Analysis" (PDF). nationalnanpa.com. April 2022. Archived (PDF) from the original on October 9, 2022. Retrieved November 30, 2022.

External links

Maryland area codes: 301/240/227, 410/443/667
	North: 717/223, 484/610/835
West: 301/240/227	410/443/667	East: 302, Atlantic Ocean
	South: 757/948
Delaware area codes: 302
Pennsylvania area codes: 215/267/445, 412, 570/272, 610/484/835, 717/223, 724, 814/582, 878
Virginia area codes: 276, 434, 540/826, 703/571, 757/948, 804/686

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[split-4] 1 2 3 Four counties were split between area code 301 and 410.
Anne Arundel County was assigned area code 410, except Laurel exchanges 210, 317, 490, 497, 498, 596, 604, 725, and 778, Marlboro exchange 952, and Fort Meade exchange 677.
Carroll County was assigned area code 410, except Mount Airy exchange 829 remained area code 301.
Howard County was assigned area code 410, except Mount Airy exchange 829 and Laurel exchanges 210, 317, 490, 497, 598, 604, 725, and 776 remained area code 301.
Frederick County remained area code 301, except Union Bridge exchange 775 and New Windsor exchange 635 was assigned 410.^[3]

[mwbw] Anne Arundel County was assigned area code 410, except Laurel exchanges 210, 317, 490, 497, 498, 596, 604, 725, and 778, Marlboro exchange 952, and Fort Meade exchange 677.

[mwcw] Carroll County was assigned area code 410, except Mount Airy exchange 829 remained area code 301.

[mwdQ] Howard County was assigned area code 410, except Mount Airy exchange 829 and Laurel exchanges 210, 317, 490, 497, 598, 604, 725, and 776 remained area code 301.

[mwdg] Frederick County remained area code 301, except Union Bridge exchange 775 and New Windsor exchange 635 was assigned 410.^[3]

[mabbs1947-1] Mabbs, Ralph (Winter 1947–1948). "Nation-Wide Operator Toll Dialing—the Coming Way". Bell Telephone Magazine. 26 (4): 181. Retrieved July 20, 2023.

[2] "New area code coming". The Baltimore Sun. November 21, 1990. p. E6.

[newareacode-3] 1 2 "New area code for eastern Maryland". The Baltimore Sun. November 1, 1991. p. 1A.

[5] "Now Area Codes Count in Md." The Washington Post. November 2, 1992. p. B9.

[6] Fazeli Fard, Maggie (October 12, 2011). "Maryland's new 667 area code goes into effect in 2012". The Washington Post . Retrieved July 23, 2012.

[7] "2022-1 NRUF and NPA Exhaust Analysis" (PDF). nationalnanpa.com. April 2022. Archived (PDF) from the original on October 9, 2022. Retrieved November 30, 2022.

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