ANdrew 8-8000

[Garrett Wollman]

<<On Thu, 9 Apr 2009 14:32:49 -0400, Sid Schweiger <sid@wrko.com> said:

> The 617-931 exchange (and other similar exchanges in every major
> city) is known as a "choke" exchange.  It is specifically designed
> to prevent overloads and cable and circuit burnouts (which used to
> occasionally happen) by routing excess calls to dead or non-existent
> trunks.

You will note that every major city has a different NXX ("exchange")
used for this purpose.  When Bell introduced "900" service, it was
originally intended for nationwide "mass calling" (rather than
pay-per-call).  The NXX (then NNX) part of the "900" number indicated
the city where the calls terminated,[1] and was numerically the same
as the NXX used for the "choke" exchange in that city.  (Hence Boston
was 900-931, Montreal was 900-790, and so on.)  The only use of this
system that I've ever heard of was a live call-in show (on a national
radio network) with President Jimmy Carter.

-GAWollman

[1] Done this way because Mother's billing systems could only handle
six digits -- this long predates today's "database dip" system.