Editing Blue box (section)

==Special codes==
Some of the special codes a person could get onto are in the chart below. "[[Numbering plan area|NPA]]" is a telephone company term for 'area code'.

Many of these appear to have been originally three-digit codes, dialed without the leading area code, and the format of destination numbers dialed to the international senders has changed at various points as the ability to call additional nations was added.<ref>{{cite book|url=http://explodingthephone.com/extras/overseas.php|title=Exploding The Phone – Extra Goodies – Overseas Dialing|author=Phil Lapsley|isbn=978-0-8021-2061-8|year=2013|publisher=Grove Press }}</ref>
* NPA+100 – Plant Test – Balance termination
* NPA+101 – Plant Test – Toll Testing Board
* NPA+102 – Plant Test – Milliwatt tone (1004{{nbs}}Hz)
* NPA+103 – Plant Test – Signaling test termination
* NPA+104 – Plant Test – 2-way transmission and noise test
* NPA+105 – Plant Test – Automatic Transmission Measuring System
* NPA+106 – Plant Test – CCSA loop transmission test
* NPA+107 – Plant Test – Par meter generator
* NPA+108 – Plant Test – CCSA loop echo support maintenance
* NPA+109 – Plant Test – Echo canceler test line
* NPA+121 – Inward Operator
* NPA+131 – Operator Directory assistance
* NPA+141 – Rate and Route Information
* 914+151 – Overseas incoming (White Plains, NY)
* 212+151 – Overseas incoming (New York, NY)
* NPA+161 – trouble reporting operator (defunct)
* NPA+181 – Coin Refund Operator
* 914+182 – International Sender (White Plains, NY)
* 212+183 – International Sender (New York, NY)
* 412+184 – International Sender (Pittsburgh, PA)
* 407+185 – International Sender (Orlando, FL)
* 415+186 – International Sender (Oakland, CA – in this era, [[area code 510|510]] was [[Telex#Teletypewriter Exchange Service|TWX]])
* 303+187 – International Sender (Denver, CO)
* 212+188 – International Sender (New York, NY)

Not all NPAs had all functions. As some NPAs contained multiple cities, an additional routing code was sometimes placed after the area code. For instance, [[area code 519|519]]+044+121 may reach the [[Windsor, Ontario|Windsor]] inward operator and 519+034+121 the [[London, Ontario|London]] inward operator {{convert|175|km|abbr=on}} distant, but in the same area code.<ref>[http://www.historyofphonephreaking.org/docs/trg/TRG-1977-Sec10-Part16-Canada.pdf Traffic Routing Guide], AT&T, 1977</ref>