Thanks to all who responded. Interesting observations.
Neal McLain wrote:
> The most "efficient" numbering plan (least amount of equipment) would be
> to assign extension numbers in three 3-digit ranges:
That's what I thought.
> This arrangement provides a total of 300 lines, enough to accommodate
> 250 apartments with spares for other uses (office, maintenance room,
> loading dock, etc.).
In my hypothetical example, I envision a copious amount of "house
phones" throughout the community, such as in front of each building,
at the pool, etc.
> Disadvantage: It's not possible to match subscriber numbers to apartment
> numbers (although, as PAT notes, this might not be a good idea anyway).
I agree for security and privacy reasons it is better NOT to have
matching intercom and apt numbers. If you want to call a specific
person, you should know their number.
>  Kempster B. Miller. "Telephone Theory and Practice" vol. 3
> "Automatic Switching and Auxiliary Equipment." New York: McGraw Hill,
> 1933, p. 129.
Thanks for the above book reference. Is it hard to find? Seems
worthwhile to check it out.
Regarding other comments, I envisioned this to be a private system
only without any outside connection. This would keep it simple and
for internal use only.
One friend suggested having a manual switchboard instead. I realized
there are two neighbors who would love to do that. They'd be good at
it because, how can I say this, they know everyone's whereabouts and
business at all times. So if you want to call Mr. Smith but he's
away, these neighbors will already know where Mr. Smith is, what he is
doing, whether or not Mrs. Smith is aware of it, etc., as well as the
status of each and every other neighbor in the complex. Not that they
would gossip or listen in on calls, they would NEVER EVER do that.
I happened to meet a retired Bell Telephone craftsmen and mentioned my
idea. He thought I was crazy. He pointed out the immense wiring and
maintenance needs of an SxS plant.
That made me realize and appreciate how far we've come with
electronics, and how complex the old Bell System was to build and run.
It's relatively easy for us today to pop in an electronic box and have
fancy phone service. It's totally another to bring together expensive
and complex SxS gear to provide service reliably. My application is
pretty basic as phone applications go, but we can see it would still
take some serious engineering and planning. Switches, wiring, and
footprint are all expensive and we don't want a 2,000 sqft room when a
500 sq ft one will do.
Modern technology has made the need for such a system obsolete. Years
ago fine apartment buildings had separate house phone systems -- more
than a plain intercom -- so the office or doormen could check in with
an apt or vice versa. Many people had message rate service* and a PBX
was a free call to call neighbors. Some buildings had answering
service switchboards which I believe Pat worked with. Anyway, today
call waiting or multiple individual phone lines eliminated the need
for a separate system. Cell phones and portable cordless phones
eliminate the need for outside and house phones -- people have their
cordless or cell phones with them and won't miss an incoming call.
Ironically the switching cost of such a system would be cheap today
but we don't even need it.
Years ago I stayed in a Miami hotel. A big function of the PBX
operators was paging guests who weren't in their room. The hotel PA
system covered all public areas. House phones were liberally placed
all over the hotel; I remember the pool area having numerous outdoor
telephone boxes (and thinking that kind of coverage was pretty neat).
The hotel PBX was a high 3 position manual board with two multiples of
the extension bank. Very small motels would have a small cord
switchboard handled by the desk clerk, but anything larger had at
least one full time operator, maybe several.
Actually in hindsight the constant paging on the PA system was a bit
tiring to other guests. I wonder if resort hotels still bother to do
that, or simply route to the room's voice mail. Today hotels have a
tiny little console the desk clerk handles in his spare time. Some
are centrex with the room numbers matching the telephone extension.
However, I was surprised recently when visiting a friend in the
hospital how often the PA system was used to page doctors. Way back
when I worked in a hospital they were converting to pagers; I presume
all doctors and key staff would carry them now. Bell had a "meet me
page" in the 1970s where the paged person would dial a special
extension and be automatically connected with the incoming call
instead of the operator manipulating cords.
*Message rate service is still offered today. But the price of a
message unit has remained stable -- 7c in my area -- for years, 7c in
1965 was more like 70c. Further today they give off peak discounts so
a weekend call might only be 3c.