TUCoPS :: Truly Miscellaneous :: nanp1947.txt

The North American Numbering Plan in 1947

From: Mark J. Cuccia <mcuccia@mailhost.tcs.tulane.edu>

As we now begin the month of October 1997, it was sometime during
October fifty years ago (in 1947), that the original area code format
was 'finalized' by AT&T. Thus, the North American Numbering Plan was

There _were_ two preliminary plans of assigning area codes. There was
a plan indicated as a map of the US in 1945 in issues of both {Bell
Laboratories Record} and {Bell System Technical Journal} magazines,
in articles on future automated toll dialing and switching - first to
be dialed by operators and later by customers. The 1945 map indicated
the (continental) US only, and indicated some 60 individual regions.
No codes were shown in the regions in the map -- only the possible
boundaries. Canada wasn't even indicated on the 1945 map in the
Bell magazine articles, although one of the articles did indicate
7-digit (2L-5N) dialing across NPA boundaries with 'protected' central
office digits where a metro area straddled an NPA boundary, and an
example cited in the article indicated that Windsor ON (Canada),
across the river from Detroit MI (USA) could be such a 'protected'
7-digit (2L-5N) dialing situation.

Another proposal was from 1946/47 would have all of the area codes in
a particular state be from a range of consecutive codes:
i.e. New York state would have used area codes 212, 213, 214, 215.

However, at some point in 1947, Bell Labs and AT&T decided to change
that plan, and instead issued the 'final' plan which has been built-on
for the past half-century. I only know that this final plan was issued
in October 1947, but I don't know which particular date in October
that a possible memo was released by AT&T regarding the nationwide
US/Canada numbering plan.

I had posted two articles to TELECOM Digest in 1996 on the preliminary
but never adopted area code plans. In April 1996 I posted a brief
article on the 1946/47 plan where a state with multiple NPA codes
would have had all of its codes from a range of consecutive codes.
And then in mid-December 1996, I posted a longer article on the
development of Operator Toll Dialing and its extension into customer
DDD (Direct Distance Dialing), and included a list of the 60 possible
regions (states, groups-of-states, portions of states) from the 1945
map of possible future area codes.

As for the 'final' plan issued in October 1947, here are the charts
showing the assignments. Linc Madison's website also has a map of the
US/Canada showing the 1947 assignments:

N0X Form (States/Provinces with only ONE code assigned)
(40 codes assigned)

201 NJ  301 MD  401 RI  501 AR  601 MS  701 ND  801 UT  901 TN
202 DC  302 DE  402 NE  502 KY  602 AZ  702 NV  802 VT  902 mrtm.prv.
203 CT  303 CO  403 AB  503 OR  603 NH  703 VA  803 SC
204 MB  304 WV  404 GA  504 LA  604 BC  704 NC
205 AL  305 FL  405 OK  505 NM  605 SD
206 WA  306 SK  406 MT
207 ME  307 WY
208 ID

N1N Form (States/Provinces with several codes assigned)
(46 codes assigned)

212 NY  312 IL  412 PA  512 TX  612 MN  712 IA  812 IN
213 CA  313 MI  413 MA  513 OH  613 ON  713 TX          913 KS
214 TX  314 MO  414 WI  514 PQ  614 OH          814 PA  914 NY
215 PA  315 NY  415 CA  515 IA          715 WI  815 IL  915 TX
216 OH  316 KS  416 ON          616 MI  716 NY  816 MO  916 CA
217 IL  317 IN          517 MI  617 MA  717 PA
218 MN          418 PQ  518 NY  618 IL
        319 IA  419 OH

Note that in 1947, there were _no_ area codes assigned from the N09,
N00, N10, nor N11 ranges. The N11 range is still unavailable for NPA
assignments, since the eight N11 codes are reserved or used for local
3-digit service codes. The N09 range of area codes were first assigned
in 1957. The N10 range of area codes were assigned to automated/dial
TWX (Teletypewriter) service beginning in 1962, and continuing through
circa 1982. Although AT&T turned (US) TWX service over to WUTCO in the
early 1970's, it wasn't until the early 1980's when WUTCO began to
switch and route (US) TWX on its _own_ network instead of over the
Bell-System's DDD Telephone Network. And although TWX still exists
(WUTCO transferred it back to AT&T circa 1990/91), it is handled via
a separate network, not 'directly' associated with the AT&T regular
telephone long-distance network, and still uses numbers of the N10
form. Therefore, beginning around 1991, the N10 format as area codes
were assigned for regular (POTS) telephone services.

The N00 format was first assigned for SACs (Special Area Codes) around
the mid-1960's, with 800 being the first N00, used for InWATS (Inward
Wide-Area Telephone Service), aka "Toll-Free" called-party pays.

Note that there were 86 codes assigned to the (at that time) 48 states
of the US, including Washington (DC), as well as the ten provinces of

Alaska and Hawaii weren't even states of the US at that time, nor were
they even indicated as even being (or intended to be) a part of the
US/Canada area code format. Canada's two northern territories, Yukon
and the Northwest Territories, weren't indicated as being a part of
the area code format, neither.

And while Mexico had been 'pseudo' NANP at one time (access to Mexico
City from the US was dialable 'as-if' it really were part of the NANP
switching/routing network) ... and for some time, certain towns along
the extreme northwestern border of Mexico were numbered and dialed
_and_ switched/routed as a part of the NANP/DDD network ... Mexico
was _not_ shown in 1947 to be intended as part of the NANP.

None of the Caribbean was indicated to be a part of the NANP in 1947.
Area Code 809 was first reserved/assigned to the Caribbean/Bermuda
area in 1958. Customer dialing between the Caribbean and the US/Canada
began to be introduced in the mid-to-late-1960's, and continuing
through the 1970's and 80's.

Newfoundland wasn't yet politically part of Canada in October 1947,
but it does seem possible that the original NPA 902 (which at that
time also served New Brunswick, in addition to Nova Scotia and Prince
Edward Island) also served Newfoundland/Labrador. In the mid-1950's,
NB and NF/LB split from 902 (which was retained for NS/PEI), into
their own 506; and then in 1962, NF/LB split off from 506 (which was
retained for NB), into its own 709.

Also note the original intent was that N0X format codes (N01 through
N08) were assigned to states/provinces which needed only one area code,
and that N1N format codes (N12 through N19) were assigned to states
and provinces which needed two or more area codes. That original
assignment plan was abandoned in the early 1950's, when assignments of
new area codes were beginning to increase.

And, note that short 'dial-pull' (lower numerical) area codes were
assigned to the more populated areas, due to the number of dialpulse
(rotary dial) CPE and switching equipment in existance in 1947. Such
shorter dial-pull area codes have fewer dial-pulses, and had been
desirable for assignment to such populated areas which would have more
incoming traffic than less populated areas.

New York City with 212
Los Angeles with 213
Dallas with 214
Philadelphia with 215
Chicago with 312
Detroit with 313
St.Louis with 314
Pittsburgh with 412

As for the 'single-NPA' states, they had N0X format codes. And even
though the middle-digit '0' is longer to dial with ten dialpulses,
the N0X area codes were assigned such that populated areas had
shorter-pull, fewer-dialpulse digits for the first and third digits
(even though the middle-digit '0' has ten total dialpulses):

201 for New Jersey
202 for DC
203 for Connecticut
301 for Maryland
302 for Delaware
401 for Rhode Island

These are all locations in the northeast or mid-Atlantic area, with
rather large metro areas, suburbs, etc., and thus a larger incoming
traffic volume. Note that rural Idaho has 208, a longer-pull code. Also
note the large number of codes which were unassigned in 1947, which are
from the longer dial-pull ranges.

While the area code format was 'finalized' in October 1947, customer
(and even operator) use of area-codes for long-distance dialing was
_QUITE_ limited. The area code format was a planning for the future,
so that every telephone line in the US and Canada would have its own
unique and distinct telephone number, for easy dialing and routing,
first by operators, and later by customers, at later dates, as new
automated toll switching (and ticketing) equipment was placed into
service, throughout the US/Canada telephone network.

Over the past fifty years, the NANP has had more codes assigned. First
there were many codes assigned throughout the 1950's and early 1960's,
due to the postwar economic and suburban 'boom', as well as the
introduction of automated customer long-distance dialing (DDD) in
addition to conversions of many manual local exchanges into dial
central offices. More customers and lines means more central office
codes. And as more central office codes are assigned, eventually new
area codes need to be created, usually by a split. Sometimes, new
area codes were created in the 1950's and early 1960's due to more
efficient trunking requirements as customer DDD was being introduced.

In the early 1960's, various conservation plans were being developed
to allow N0X/N1X format codes for local central office codes (to be
needed in some large populated areas, sometime by the mid-1970's), and
for NNX format codes to be used as area codes, sometime by the mid-to-
late-1990's. So-called 'interchangeable' NPA codes (NNX format) have
indeed been introduced beginning in 1995, and have been assigned at
rates never previously seen, surpassing the early rush of area code
assignments in the 1950's and early 1960's.

Our ten-digit numbering scheme (NXX-NXX-xxxx) in the NANP is expected
to exhaust all available (POTS) area codes sometime in the first-half
of the 21st Century. At first it was estimated to happen by 2050, but
because of the current rate of assignment of NPA codes, some have
pushed that date earlier to 2010. However, if local number portability
amongst the competitive local telcos is properly introduced over the
next ten years, or if central-office-code sharing takes place among
the various competitive telcos, it may be possible to reduce the rate
of area code assignments.

There are frequently questions as to why so many countries or
territories are included in a single numbering plan (CCITT/ITU Country
Code +1), rather than the US, Canada, and each individual Caribbean
island each having unique/distinct country-codes. In 1947, much of
Canada's telephone industry was directly associated with the US
telephone industry. AT&T did own a portion of Bell Canada; and AT&T's
Western Electric, along with Bell Canada, owned Northern Electric
(later known as Northern Telecom, now known as Nortel). The Caribbean
was intended to be added in 1958. Plans to incorporate Mexico into the
DDD network also existed since the late 1950's, and were first
introduced around the early-to-mid-1960's. The CCITT/ITU plans for
country-codes for each telephone country/network in the world wasn't
really introduced until around 1964 (although there was a preliminary
1960 plan for country codes for Europe, North Africa, and nearby Asian

In closing, while there were 86 area codes assigned for the NANP in
October 1947, fifty years later, on 1-October-1997, I am counting at
least 212 active "POTS" (non-SAC) area codes in the NANP, even if only
in permissive dialing. And the increase in new NPA codes is far from
over or even slowing down.

NWORLASKCG0 (BellSouth #1AESS Class-5 Local "Seabrook" 504-24x-)
NWORLAIYCM1 (BellSouth-Mobility Hughes-GMH-2000 Cellular-MTSO NOL)
NWORLAMA0GT (BellSouth DMS-100/200 fg-B/C/D Accss-Tandem "Main" 504+)
NWORLAMA20T (BellSouth DMS-200 TOPS:Opr-Srvcs-Tandem "Main" 504+053+)
NWORLAMA04T (AT&T #4ESS Class-2 Toll 060-T / 504-2T "Main" 504+)
JCSNMSPS06T (AT&T #5ESS OSPS:Operator-Services-Tandem 601-0T 601+121)


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