TELECOM Digest OnLine - Sorted: Re: NN0 Central Office Codes

Re: NN0 Central Office Codes

Mark Roberts (
Tue, 08 Nov 2005 03:14:35 -0000

Neal McLain <> had written:

It didn't work out that way ...

> Many NN0 codes were assigned as central office codes whenever and
> wherever they were needed, without regard to their positions on Chart 5.

> Examples that come to mind:

> 702-870 (#3 on the list) ca. 1989 Las Vegas
> 312-990 (#32 on the list) ca. 1988 Hinsdale
> 201-460 (#36 on the list) ca. 1982 Lyndhurst
> 414-730 (#52 on the list) ca. 1986 Appleton
> 214-680 (#54 on the list) ca. 1983 Dallas

I can add, all circa 1984 from Houston:

The first two were in the JAckson switch (Montrose, River Oaks,
the Museum District) and the 520 prefix is an obvious candidate for
"lookalike" status. At the time, Southwestern Bell had been so
regular in grouping exchanges by the first two digits that Key
Maps, a local company, was able to publish maps identifying
exchanges by the first two digits only in most cases.

I can personally attest to 713-630 because that was used for the PBX
at KTRH radio, where I worked at the time. While most of the "public"
numbers for KTRH were standard JAckson numbers -- I'm pretty sure the
main call-in number was 526-5874 (KTRH) -- our internal extensions
were of the form 630-3xxx.

The second two were in the NAtional office (Greenway Plaza and the
Galleria area). They, of course, looked nothing like the usual
62x-xxxx numbers in that area.

> Curiously (as Mark Roberts noted in TD 24:482), 530 (#1 on the list)
> was in service -- at least briefly -- in California in 1965, a decade
> before Chart 5 was published.

As an interim measure, until I can write up some better-looking pages,
I have put the 1964 and 1965 exchange maps online from the Pacific
Bell Oakland ("East Bay") directory.

I should note that there was a *series* of maps, designed to indicate
the message-unit charges from the East Bay "exchange" (Berkeley,
Main-Piedmont, Alameda, Fruitvale, Trinidad) to other rate centers in
the region. Each East Bay rate center had its own map. I've scanned
the ones for Main-Piedmont to provide a comparison, and to more
clearly show the "530" prefix in the Fruitvale area in the 1965 map.

On the map:
A = Berkeley
B = Main-Piedmont
C = Alameda
D = Fruitvale
E = Trinidad

Sometime in 1965 -- I have not yet nailed down when -- there was a
spinoff into a new switch, affecting primarily the Fruitvale rate
center, but also the eastern part of Main-Piedmont. Approximately the
eastern half of the Fruitvale rate center plus the little corner of
Main-Piedmont went into the switch now known as OKLDCA13DS0. This
split accounts for the new 339 and 531 prefixes. As I previously
mentioned, 530 popped up only for that year. Later, however, 530
"joined" 531 in eastern Fruitvale and is an active prefix today
(several of my neighbors have it including one who moved to this area
in the 1970s).

Another thing I need to nail down is how extensive the cutover was at
first. Today, the Fruitvale OKLACA13DS0 area extends all the way to
Interstate 580 and over to the junction of 580 and Highway 13. It may
be that the original cutover area was smaller, and areas were added
later (e.g. along MacArthur Boulevard).

This distinction, of course, is NOT shown on the maps that I scanned,
and consequently will have to be inferred from listings, newspaper
ads, etc.

Anyhow, here are the maps. There were several prefixes added between
1964 and 1965, not just in Oakland:

Mark Roberts | "I know you know the situation is past critical."
Oakland, Cal.| -- FEMA staff member Marty Bahamonde, in New Orleans
NO HTML MAIL | "Anything specific I need to do or tweak?"
| -- FEMA director Michael Brown replies to that e-mail

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