Date: Tue, 29 Apr 2003 21:06:51 CDT From: Mark J Cuccia Subject: NPA and C.O. Code Numbering Rules Over the Years Mike O. wrote: > I vaguely remember a "rule" the phone company had when they made area > codes available to the public dial system (1960?). The primary rule > was that the exchange (prefix) could not have a zero or one, that was > reserved for area codes. But, they also said that future area codes > (when they ran out of zero and one, in a projected 25 years) would use > 2 and 3, as the center digit. Then 4 and 5, etc. I don't know how > valid this was, or if it was just an "urban legend" from that era, > but it may shed some light on numbering schemes. And Pat added: > Area codes began being used in the 1950's in a few places, even while > many places were still entirely manual in operation. The rule was no > zeros or ones as the middle digit in prefixes, and no zeros as the > right, or last digit in a prefix. That's largely because the early or > original area codes all had zeros or ones as the middle digit. There > was also a rule that states which had only one area code for the entire > state had a number which used zero as the middle digit; a second or > subsequent area code in the same state had one as the middle digit. What Pat says is "essentially" true ... but here is MUCH more detail and history, as one would expect coming from me! :-) It was October 1947 when Bell Labs and AT&T "finalized" the plan for area codes to be used initially in Nationwide Operator Toll Dialing, and ultimately Customer Direct Distance Dialing. There were preliminary plans hashed out in the immediate postwar years of 1945-47, which the final plans developed further. The Oct.1947 "rule" was that states/provinces with ONE and ONLY ONE area code would have a '0' in the middle. State/provinces with multiple area codes would have a '1' in the middle. Larger metro areas which were expected to have a large volume of incoming calls would have "lower digit" / "shorter dial-pull" / "fewer dial-pulse" formatted area codes. Of course, Washington DC (a single 'state-like' entity has fourteen pulses, a longer "pull" of the '0' in the middle, but because there was ONE area code for the DC state-like entity, the original rule of having a '0' as the middle digit applies. Similarly, NJ had only ONE area code as of Oct.1947, 2-0-1, with thirteen pulses, a longer pull of '0' in the middle (ten-pulses), but the state had ONLY ONE area code, thus the middle-digit of '0'. BUT... of the N0X format area codes, these area codes are two of the "lowest/shortest/fewer"... At that time, many operator "dials" still sent out dialpulses, whether they used a rotary dial or a "keyset", thus fewer dialpulses were desirable for frequently called area codes / locations. Also at the time, there no area codes were of the N09 format. The first N09 area codes first began around 1957, ten years after the finalized format of area codes was announced in Oct.1947. There *NEVER* have been any Area Codes (nor "POTS" office codes) of the N11 format, as N11 had already been in use as 3-digit special purpose codes (411 Information, 611 Repair, etc) in Panel/Crossbar cities. These codes are still in use for these special purposes today, although in the 1980s/90s, *some* telcos (mainly Pac/NV*Bell in CA/NV and GTE-BC Tel in British Columbia) were known to have used 7-digit special "local-only" numbers for Business Office and Repair *specific departments* (i.e., resi, business, coin, payment arrangments, new orders/features, etc), as 611-XXXX and 811-XXXX. There were NO area codes of the N10 nor N00 format in the 1940s/50s. The N10 format codes first were used for Telco Dial-TWX for new 4-Row Keyboard 7/8-level ASCII 100-speed TWX, starting in the early 1960s. 3-Row Kybd 5-level Baudot 60-speed TWX which had existed since 1931 was automated at the same time by adding modems and dials to the TTYs and integrating them into the DDD telephone network by giving them POTS-like telephone numbers using "POTS" area codes. 3-Row TWX began to disappear as 4-Row TWX devloped. Western Union took over the marketing of TWX by US Federal Government orders in the early 1970's but it wasn't until 1981 when TWX in the US was completely removed from the US-portion of the DDD telephone network and instead completely re-routed over Western Union's own Telex network. The N10 format codes no longer had *ANY* meaning on the US-part of the DDD telephone network (although WUTCO still had TWXes numbered with N10 format codes on the WUTCO Telex-I/II network), but it wasn't until the early 1990s when Bellcore first assigned real POTS telephone area codes of the N10 format. The first use of N00 area codes was with 800 (InWATS toll-free) in the mid-1960's. The N00 format has continued to be used for "special" non-geographic NANP-wide functions. 900 for PAY-per-call, 700 for carrier services, 600 for Canadian services, 500 for personal numbering. This N00 format has since become a subset of the NZZ format, where the middle and third digits are "identical" for an even broader format of (future) special function codes. Current uses of the broader NZZ format are used for the additional toll-free codes 888, 877, 866, and future 855, 844, 833, 822. Central Office codes (the 'D-E-F' position of a ten-digit number) never had '0' or '1' as their middle or 'E' position digits in the "old" days. This is why area codes were initially chosen to be N0X and N1X format, so that one could dial just seven or just ten, and the (crossbar) equipment could tell by the second digit dialed whether to expect seven or ten-digits total. One of the reasons that there were hadn't been any N0X nor N1X format c.o.codes was that there were no letters on the '0' or '1', back when 2L-5N exchange-name dialing was in use. Also, NN0 format office codes were HIGHLY DISCOURAGED for DECADES, initially because the '0' (zero) third digit might be confused with the letter 'O' (oh). But this "rule" wasn't always adhered to completely. The Los Angeles Metro Area even as far back as the 1930s had some "EXchange" name plus '0' (zero) office codes! New Orleans had a temporary use (1959) of "WHitehall-0" (940). The first use of area codes by Operators in Operator Toll Dialing that I've seen documented, was in early 1949, when San Francisco/Oakland Bay area operators with AT&T/Pacific Telephone were able to *DIAL* (or 'key') directly to NYCity and some other east coast major cities, as NPA+2L-5N. The first documented/known use of CUSTOMER dialing with area codes began in Nov.1951 from Englewood and Teaneck NJ, where they could dial about fifteen major metro areas throughout the US. (There are articles and reports in the TELECOM Digest Archives on the Englewood DDD experiment that started in November 1951). In the late 1950's, as the postwar cultural and technological boom was in high year in the US (and Canada), AT&T was beginning to become worried that they might run out of "numbering/code" resources. There are documents in the TELECOM Digest Archives that I transcribed back in 1996, from that late 1950's time-frame describing the worries of AT&T. More and more manual central offices were being cut-over to dial. There was the baby-boom and suburban expansion ... fewer customers of party-lines ... radiotelephony and automated paging was becoming common among the wealthy and business types who relied on such ... PBXes and Centrex was becoming automated and "integrated" into the basic numbering plan, where each and every hotel room, hospital room, office desk, etc. would have a "real" POTS 7/10 digit telephone number for direct-in-dialing ... Business (and residential customers) were having multiple lines, in many businesses, even back in the 1950's, there were now dial-in "dataphones" -- i.e., computer modems ... and so forth. All of these new technologies were "hinted at" in the 1940's, but nobody could predict the virtual explosion of these happening as such in the 1950's. Bell decided that it would get rid of "EXchange name" dialing and go to ANC (All Numeric Calling), which took twenty years in some areas to convert to ... but also, in the late 1950's/early 1960's, it was decided that "by the 1970s especially in NY and Los Angeles", there would need to be N0X and N1X format c.o.codes so that 212 (NY) and 213 (Los Angeles) could have longer lives, and that "by the 1990s" there would need to be NNX format Area Codes as all of the N0X and N1X format area codes might be used up. These predictions of the late 1950's mostly came true "on schedule". Los Angeles did adopt N0X and N1X format c.o.codes in the early 1970's, New York City adopted such "interchangeable" office codes in the early 1980's, and other major metro areas adopted these format c.o.codes throughout the 1980's and continuing. NNX format area codes were added to the N0X and N1X format to form the more generalized NXX format for area codes by Jan.1995, again, more-or-less "on schedule". INITIALLY, in the early 1960's, the "assignment order" for new NNX format area codes would have been to use NN0 format area codes. Remember I mentioned earlier that AT&T *HIGHLY DISCOURAGED* the use of NN0 codes for c.o.codes for DECADES. This turned out to be somewhat of a 'blessing' because many areas really didn't add many NN0 format c.o.codes over the decades, even during more recent ones, prior to 1995. Also, if you look at all new (post-1995) NNX format area codes, MOST of them, or the largest block of them at least, are of the N-N-0 format when compared with N--N--other-last-digit formats. In the 1960's/70's/80's, there was to have been a "specific order" of assigning NN0 format area codes when they were expected to first be needed in the 1990's. After the 63 NN0 codes (950 was *NOT* to be assigned as an "area code" since it has a universal function as a special c.o.code for dial-up access to "other common carriers") were assigned/activated as area codes, then OTHER NNX codes could then be used, but there was no special "ordering" of them. The "order" of assignments for NN0 area codes had been published in several AT&T/Bell System publications, including Notes on the Network/Distance Dialing (1968, 1975, 1980, 1983, 1986), and in several Bell System Letters and Bell System Practices of the 1960s/70s timeframe. Here is the assignment order as was *originally* intended back in the 1960s/70s/80s, from first thru sixty-third; the additional notes are what has happened to that area code numeric since 1995: 260 (which was assigned to part of IN's 219 3-way split in 2002) 480 (which was assigned to part of AZ's 602 3-way split in 1999) 520 (which was assigned to 1995's split of 602 AZ) 590 NOT ASSIGNED (see below) 650 (which was assigned to 1997's split of 415 CA) 220 (not assigned; ?? potentially reserved for relief of 440 OH ??) 250 (which was assigned to 1996's split of 604 BC) 490 NOT ASSIGNED (see below) 660 (which was assigned to 1997's split of 816 MO) 680 (not assigned; ?? potentially reserved for relief of 315 NY ??) 720 (which was assigned to 1998's overlay of 303 CO) 730 (not assigned; ?? potentially reserved for relief of 618 IL ??) 850 (which was assigned to 1997's split of 904 FL) 940 (which was assigned to part of TX's 817 3-way split in 1997) 230 (not assigned; ?? potentially reserved for relief of 626 CA ??) 240 (which was assigned to 1997's overlay of 301 MD) 290 NOT ASSIGNED (see below) 470 (assgnd- future addtnl overlay to existing Atlanta Metro overlays) 550 (not assigned; ?? potentially reserved for relief of 702 NV ??) 580 (which was assigned to 1997's split of 405 OK) 740 (which was assigned to 1997's split of 614 OH) 930 (not assigned; ?? potentially reserved for relief of 812 IN ??) 450 (which was assigned to 1998's split of 514 PQ) 760 (which was assigned to 1997's split of 619 CA) 880 *** see note below *** 570 (which was assigned to 1998's split of 717 PA) 380 (assigned for future date-not-defined overlay of 614 OH) 460 (not assigned; ?? potentially reserved for relief of 204 MB ??) 980 (which was assigned to 2001's overlay of 704 NC) 860 (which was assigned to 1995's split of 203 CT) 960 NOT ASSIGNED (see below) 990 NOT ASSIGNED (see below) 970 (which was assigned to 1995's split of 303 CO) 350 (not assigned; ?? potentially reserved for relief of 209 CA ??) 540 (which was assigned to 1995's split of 703 VA) 820 (not assigned; ?? potentially reserved for relief of 805 CA ??) 840 (not assigned; ?? potentially reserved for relief of 512 TX ??) 690 NOT ASSIGNED (see below) 770 (which was assigned to 1995's split of 404 GA) 890 NOT ASSIGNED (see below) 320 (which was assigned to 1996's split of 612 MN) 370 NOT ASSIGNED (see below) 790 NOT ASSIGNED (see below) 280 (not assigned; ?? potentially reserved for relief of 240 MD ??) 640 (not assigned; ?? potentially reserved for relief of 609 NJ ??) 750 (not assigned; ?? potentially reserved for relief of 808 Hawaii ??) 270 (which was assigned to 1999's split of 502 KY) 430 (which is this year's, 2003's overlay to 903 TX) 630 (the 1995 overlay to Chicago for cellular, 1996 split of 708 IL) 670 (assgnd to Saipan/Mariana Isl's incorporation in the NANP in 1997) 560 (not assigned; ?? potentially reserved for relief of 907 Alaska ??) 330 (which was assigned to 1996's split of 216 OH) 340 (assigned to US Virgin Isls split from 809 in 1997) 390 NOT ASSIGNED (see below) 620 (which was assigned to 2001's split of 316 KS) 830 (which was assigned to part of TX's 210 3-way split in 1997) 920 (which was assigned to 1997's split of 414 WI) 360 (which was assigned to 1995's split of 206 WA) 440 (which was assigned to 1997's split of 216 OH) 780 (which was assigned to 1999's split of 403 AB) 870 (which was assigned to 1997's split of 501 AR) 420 (not assigned; ?? potentially reserved for relief of 808 Hawaii ??) 530 (which was assigned to 1997's split of 916 CA) In the early 1990s, Bellcore and the NANP Telco industry forums decided that with 1995's need to introduce "interchangeable" (i.e., NNX format) area codes, that instead of just starting off with NN0, that rather they'd go with the full batch of NNX at the start. However, as I mentioned earlier, there are more N-N-0 ones than other N-N- other-last-digits. Also, by 1994, the ATIS-INC-ICCF (industry forums) and (Bellcore) NANPA decided that N9X format codes would be reserved for expansion purposes whenever the NANP would need to go to something longer than ten-digits, and that the 96X and 37X formats would be reserved as well for some future need (presently undefined) which might require a complete block of ten-consecutive codes. A note about 880: In 1995, Bellcore-NANPA assigned 880 for use by foreign (non-NANP) overseas customers to be able to call (at charge) NANP-based 800 "toll-free" numbers, by "replacing" the 800 with 880, as +1-880-seven-digits. (881 was also assigned as a "replace" code for international calling party pays to call NANP 888 "toll-free" in 1996, and 882 was assigned in 1998 as the international calling party pays replace code for NANP 877 "toll-free". There was never assigned such a "replace" code for NANP 866 "toll-free" nor for any future NANP toll-free SAC codes. And the ATIS-INC forum wants to actually *RECLAIM* 880, 881, 882 from their current defined uses, and the international caller "might" thus call NANP "toll-free" numbers (whether for free or at charge) using the "regular" 800/888/877/etc. code in +1/NANP. The currently intended future use of 880, 881, 882, 883, 884, 885, 886, 887, and then 889, is for FUTURE (post 855 then 844 then 833 then 822) NANP toll-free numbers. There is of course, a *LOT* more that I could go "on-and-on ad-nauseum" about, but I'll close out here with a transcribed chart of the original eighty-six NPA (area code) assignments of the original "finalized" draft plan of October 1947, some 55+ years ago. Also, DISCLAIMER ... I certainly HOPE that my typing here has mostly been correct, and hope that I do NOT have any significant/factual errors due to any possible typo's ... So, without further ado, here is the 1947 area code chart, broken down into N0X and N1X: N0X Form, States/Provinces with ONE and 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 US: 48-states/DC, Canada: nine-provinces (also NF/LB) -- are the ONLY parts of the NANP at this time (Alaska, Hawaii, Caribbean, Mexico, Pacific Islands, etc, not intended to have area codes until years later) *NO* codes of the form N09, N00, N10, or N11 assigned at this time; N11 reserved for 3-digit local service codes (*NO* special functions of TWX, toll-free, etc, at this time) Mark J. Cuccia mcuccia@tulane.edu New Orleans LA USA [TELECOM Digest Editor's Note: In addition to its regular place in the back issues files of the Digest, this special report by Mark will be filed in the telecom-digest.org/history area of the web site for review by interested parties. Thank you, Mark, for your usual, excellent presentation. PAT]