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<p><b>Area code 423</b> is a telephone <a href="Area_code" class="mw-redirect" title="Area code">area code</a> in the <a href="North_American_Numbering_Plan" title="North American Numbering Plan">North American Numbering Plan</a> for the <a href="U.S._state" title="U.S. state">U.S. state</a> of <a href="Tennessee" title="Tennessee">Tennessee</a>. It comprises two disconnected areas of <a href="East_Tennessee" title="East Tennessee">East Tennessee</a> (as well as portions of <a href="Van_Buren_County%2C_Tennessee" title="Van Buren County, Tennessee">Van Buren</a> and <a href="Sequatchie_County%2C_Tennessee" title="Sequatchie County, Tennessee">Sequatchie</a> counties in <a href="Middle_Tennessee" title="Middle Tennessee">Middle Tennessee</a>) that are separated by <a href="Area_code_865" title="Area code 865">area code 865</a>.

</p><p>Principal cities in the northern part of the area code region are <a href="Morristown%2C_Tennessee" title="Morristown, Tennessee">Morristown</a>, <a href="Greeneville%2C_Tennessee" title="Greeneville, Tennessee">Greeneville</a>, <a href="Kingsport%2C_Tennessee" title="Kingsport, Tennessee">Kingsport</a>, <a href="Johnson_City%2C_Tennessee" title="Johnson City, Tennessee">Johnson City</a>, and <a href="Bristol%2C_Tennessee" title="Bristol, Tennessee">Bristol</a> (more commonly known as the <a href="Tri-Cities_(Tennessee)" class="mw-redirect" title="Tri-Cities (Tennessee)">Tri-Cities</a> region). The principal cities in the south are <a href="Chattanooga%2C_Tennessee" title="Chattanooga, Tennessee">Chattanooga</a> and <a href="Cleveland%2C_Tennessee" title="Cleveland, Tennessee">Cleveland</a>.

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<div class="mw-heading mw-heading2"><h2 id="History">History</h2></div>

<p>When the <a href="American_Telephone_and_Telegraph_Company" class="mw-redirect" title="American Telephone and Telegraph Company">American Telephone and Telegraph Company</a> created the first nationwide <a href="Telephone_numbering_plan" title="Telephone numbering plan">telephone numbering plan</a> for <a href="Operator_Toll_Dialing" title="Operator Toll Dialing">Operator Toll Dialing</a>, the predessessor of the North American Numbering Plan, in 1947, Tennessee was a single numbering plan area (NPA) with <a href="Area_code_901" title="Area code 901">area code 901</a>. In 1954, 901 was reduced to <a href="West_Tennessee" title="West Tennessee">West Tennessee</a>, while the rest of the state received <a href="Area_code_615" class="mw-redirect" title="Area code 615">area code 615</a>.

</p><p>In 1995, the eastern portion of 615, including <a href="Knoxville" class="mw-redirect" title="Knoxville">Knoxville</a>, Chattanooga, and the Tri-Cities, was split off with area code 423. This was the first new area code in the state in 41 years.

</p><p>The boundary between 423 and 615 roughly followed the line between the <a href="Eastern_Time_Zone" title="Eastern Time Zone">Eastern</a> and <a href="Central_Time_Zone" title="Central Time Zone">Central</a> time zones; generally, Tennessee's share of the Eastern Time Zone was in 423. As a result, the state's three area codes were roughly coextensive with the traditional <a href="Grand_Divisions_of_Tennessee" title="Grand Divisions of Tennessee">Grand Divisions of Tennessee</a>. The new 423 served almost all of East Tennessee, with 615 serving <a href="Middle_Tennessee" title="Middle Tennessee">Middle Tennessee</a> and 901 serving <a href="West_Tennessee" title="West Tennessee">West Tennessee</a>.

</p><p>The <a href="Tennessee_Regulatory_Authority" class="mw-redirect" title="Tennessee Regulatory Authority">Tennessee Regulatory Authority</a> intended this configuration to be a long-term solution. However, within only three years, 423 was already close to exhaustion due to the proliferation of cell phones and pagers, particularly in Knoxville and Chattanooga. It soon became apparent that East Tennessee needed another area code, even though this would have forced many residents and businesses to change their numbers for the second time in a decade.

</p><p>On November 1, 1999, <a href="Area_code_865" title="Area code 865">area code 865</a> was created for Knoxville and most of the central portion of East Tennessee. Permissive dialing of 423 continued across East Tennessee until April 22, 2000.<sup id="cite_ref-nanp183_1-0" class="reference"><a href="#cite_note-nanp183-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> Relief planning discovered that the Tri-Cities had too much traffic to follow Knoxville into 865, but were not large enough for a new area code through a three-way split. This left the Tennessee Regulatory Authority with two options–a split plan that would create two <a href="Geographic_contiguity" title="Geographic contiguity">non-contiguous</a> sections of 423, or implement 865 as an <a href="Overlay_complex" title="Overlay complex">overlay complex</a> for all of East Tennessee. The Tennessee Regulatory Authority selected the first option, since overlays were a new concept at the time, and had encountered some resistance due to the need for <a href="Ten-digit_dialing" title="Ten-digit dialing">ten-digit dialing</a>.

</p><p>Normal practice would have called for Knoxville to retain 423, as it was the largest city in the numbering plan area. However, the Tennessee Regulatory Authority asked for Knoxville to receive 865 because on an alpha-numeric telephone keypad, those numbers correspond to <i>VOL</i> (<i>Volunteers</i>) the nickname for the sports teams at the <a href="University_of_Tennessee" title="University of Tennessee">University of Tennessee</a>.<sup id="cite_ref-Brewer_2-0" class="reference"><a href="#cite_note-Brewer-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-TRA_3-0" class="reference"><a href="#cite_note-TRA-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup>

</p><p>This created one of the few area codes in the nation that is not contiguous, as 865 is almost entirely surrounded by 423 except on the east. Although this seemed to be a temporary solution, the <a href="North_American_Numbering_Plan_Administration" class="mw-redirect" title="North American Numbering Plan Administration">North American Numbering Plan Administration</a> initially determined that the reconfigured 423 would not be exhausted until around 2010.<sup id="cite_ref-nanp183_1-1" class="reference"><a href="#cite_note-nanp183-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> With the 2002 implementation of <a href="Number_pooling" class="mw-redirect" title="Number pooling">number pooling</a> in the southern portion of the area code (the Chattanooga area), the Tennessee Regulatory Authority projects that 423 will remain in its unusual, non-contiguous state until 2025. Even after that, an overlay of 423 was approved ensuring the configuration will be maintained.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup>

</p><p>On May 30, 2023, the <a href="Tennessee_Public_Utility_Commission" title="Tennessee Public Utility Commission">Tennessee Public Utility Commission</a> approved the all-service overlay of area code 423 with <b>area code 729</b>. <a href="Permissive_dialing" title="Permissive dialing">Permissive ten-digit dialing</a> started on August 5, 2024, and became mandatory on August 5, 2025. Central office code activations for 729 may begin on September 5, 2025, the official in-service date, provided that all assignable 423-central office codes have been exhausted.<sup id="cite_ref-PL629_5-0" class="reference"><a href="#cite_note-PL629-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.nanpa.com/sites/default/files/planning_letters/PL-183.pdf">"Planning Letter 183: Geographic Split of 423 (Tennessee) Numbering Plan Area (NPA); addition of 865 NPA"</a> <span class="cs1-format">(PDF)</span>. NANPA. July 22, 1999<span class="reference-accessdate">. Retrieved <span class="nowrap">February 15,</span> 2025</span>.</cite></span>

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<li id="cite_note-Brewer-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-Brewer_2-0">^</a></b></span> <span class="reference-text">See Brewer, Bill. "<a rel="nofollow" class="external text" href="https://web.archive.org/web/19991003042549/http://areacode-info.com/headline/1999/tn990417.htm">423 Area Code To Become VOL In 9 ET Counties</a>." <i>Knoxville News-Sentinel</i>. April 17, 1999.</span>

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<li id="cite_note-TRA-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-TRA_3-0">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.state.tn.us/tra/pressr/1999/vol865.pdf">Tennessee Regulatory Authority press release</a>, April 29, 1999</span>

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<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.nationalnanpa.com/reports/2023-1NPAExhaustProjectionsFinal.pdf">"2023-1 NRUF and NPA Exhaust Analysis"</a> <span class="cs1-format">(PDF)</span>. <i>nationalnanpa.com</i>. April 2023<span class="reference-accessdate">. Retrieved <span class="nowrap">June 26,</span> 2023</span>.</cite></span>

</li>

<li id="cite_note-PL629-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-PL629_5-0">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.nanpa.com/sites/default/files/planning_letters/PL-629.pdf">"Planning Letter 629: NPA 729 and 423 All-Services Overlay (Tennessee)"</a> <span class="cs1-format">(PDF)</span>. NANPA. November 6, 2024<span class="reference-accessdate">. Retrieved <span class="nowrap">February 15,</span> 2025</span>.</cite></span>

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<li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.wbir.com/article/news/local/10-digit-dialing-in-east-tennessee-starts-feb-5/51-85f0e573-4855-420d-9f5a-1d6b23e238eb">"10-digit dialing in East Tennessee starts Aug. 5. Here's what you need to know"</a>. <i>wbir.com</i>. January 6, 2025<span class="reference-accessdate">. Retrieved <span class="nowrap">January 11,</span> 2025</span>.</cite></span>

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<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.nanpa.com/resources/area-code-maps">"Area Code Maps"</a>. NANPA.</cite></li></ul>

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<caption><a href="Tennessee" title="Tennessee">Tennessee</a> area codes: , <a href="Area_codes_615_and_629" title="Area codes 615 and 629">615/629</a>, <a href="Area_code_731" title="Area code 731">731</a>, <a href="Area_code_865" title="Area code 865">865</a>, <a href="Area_code_901" title="Area code 901">901</a>, <a href="Area_code_931" title="Area code 931">931</a>

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<td width="30%" style="text-align:center;"><b>North</b>: <a href="Area_code_606" title="Area code 606">606</a>, <a href="Area_code_276" title="Area code 276">276</a>

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<td width="30%" style="text-align:center;"><b>South</b>: <a href="Area_code_256" class="mw-redirect" title="Area code 256">256</a>, <a href="Area_codes_706_and_762" title="Area codes 706 and 762">706/762</a>

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<td colspan="3" style="text-align:center;"><a href="Alabama" title="Alabama">Alabama</a> area codes: <a href="Area_codes_205_and_659" title="Area codes 205 and 659">205/659</a>, <a href="Area_code_251" title="Area code 251">251</a>, <a href="Area_codes_256_and_938" title="Area codes 256 and 938">256/938</a>, <a href="Area_code_334" title="Area code 334">334</a>

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<td colspan="3" style="text-align:center;"><a href="Georgia_(U.S._state)" title="Georgia (U.S. state)">Georgia</a> area codes: <a href="Area_code_229" title="Area code 229">229</a>, <a href="Area_code_404" title="Area code 404">404</a>, <a href="Area_code_478" title="Area code 478">478</a>, <a href="Area_codes_678%2C_470%2C_and_943" title="Area codes 678, 470, and 943">678/470/943</a>, <a href="Area_codes_706_and_762" title="Area codes 706 and 762">706/762</a>, <a href="Area_code_770" title="Area code 770">770</a>, <a href="Area_code_912" title="Area code 912">912</a>

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<td colspan="3" style="text-align:center;"><a href="Kentucky" title="Kentucky">Kentucky</a> area codes: <a href="Area_codes_270_and_364" title="Area codes 270 and 364">270/364</a>, <a href="Area_code_502" title="Area code 502">502</a>, <a href="Area_code_606" title="Area code 606">606</a>, <a href="Area_code_859" title="Area code 859">859</a>

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<td colspan="3" style="text-align:center;"><a href="Virginia" title="Virginia">Virginia</a> area codes: <a href="Area_code_276" title="Area code 276">276</a>, <a href="Area_code_434" title="Area code 434">434</a>, <a href="Area_codes_540_and_826" title="Area codes 540 and 826">540/826</a>, <a href="Area_codes_703_and_571" title="Area codes 703 and 571">703/571</a>, <a href="Area_codes_757_and_948" title="Area codes 757 and 948">757/948</a>, <a href="Area_codes_804_and_686" title="Area codes 804 and 686">804/686</a>

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<td colspan="3" style="text-align:center;"><a href="North_Carolina" title="North Carolina">North Carolina</a> area codes: <a href="Area_code_252" title="Area code 252">252</a>, <a href="Area_codes_336_and_743" title="Area codes 336 and 743">336/743</a>, <a href="Area_codes_704_and_980" title="Area codes 704 and 980">704/980</a>, <a href="Area_code_828" title="Area code 828">828</a>, <a href="Area_codes_910_and_472" title="Area codes 910 and 472">910/472</a>, <a href="Area_codes_919_and_984" title="Area codes 919 and 984">919/984</a>

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