In message , at
11:36:50 on Tue, 4 Jan 2005, Martin Underwood remarked:
Surely all phones have always had a very ready source of power: the standing
voltage on the phone line. Couldn't that have been used to power coin-return
etc in Button A/B phones? Or was it just that there was enough current
available?

A combination of the latter, and "why complicate things" if a cheap
mechanical solution works.
--
Roland Perry