In message , at
14:57:34 on Sat, 1 Jan 2005, Martin Underwood remarked:
Nowadays no buttons
are needed because the coin is automatically consumed if the call is
answered (equivalent to pressing A) and automatically returned (if not used)
when the handset is replaced (equivalent to pressing B). I'm not sure why
this functionality wasn't included in old callboxes: surely it wasn't
difficult even in valve-amplifier and relay days.

Almost certainly because the button A/B callboxes weren't powered. All
the work was done by pressing the buttons very hard. If it was necessary
to count coins, fore example on a long distance call, the operator (who
would be needed pre-STD) would literally listen-in and count while the
line was interrupted every time you put a coin in. When that money as
used up the operator would have to come back to you.
--
Roland Perry