In message , at 23:10:09 on
Sun, 19 Jul 2009, Charles Ellson remarked:

There *is* an underlying technical issue, in that out-of-area codes
don't scale, because they involve running wires from one exchange to
the other.

Surely it's all done with software now? In any case, the exchanges are
now connected by high bandwidth glass, not copper wire.

The software switches calls within the exchange, but they have to get
there first.

I'm not sure if it does any more. ISTR the exchange "owning" the
number now rejects the call and instructs the originating exchange
where to send it (all done in milliseconds) BICBW.

That's what they do for number portability. Perhaps it's also used for
out-of-area numbers, but I'm not aware of it.

The older version
on some exchanges required use of a directory number at the exchange
actually serving the subscriber to which calls were silently diverted
by the exchange which "owned" the number; IIRC that became unneccesary
once everything was replaced by System X or newer.

Call diversion tends to be charged by use, whereas an out of area number
would be a flat rate.

The originating exchange can only send to the receiving
exchange specified by the code (there won't be an "exception routing
table" for the out-of-area numbers). And that exchange then has to
deliver the call to a distant POTs line.

ITYF that like 0345, 0845 etc. it can deliver to a "numberless"
circuit.

The circuit still has to deliver to the premises via POTs. Geographic
numbers are done by ISDN, and/or the receiving party collecting the
calls from the exchange.
--
Roland Perry