Martin Underwood wrote to uk.transport.london on Sat, 1 Jan 2005:

- Button A / Button B or pay-on-answer callboxes: remember those wretched
pips

The first call we received after we'd gone to STD (Subscriber Trunk
Dialling - before then, we'd had no dialling of any kind) was from a
phone-box, and my mother was most upset at the thought of "That horrid
noise" whenever the phone rang.....

But do you remember "the pips" that would warn you when you'd been
talking for three minutes on a long-distance call (trunk call, they were
called), since such calls were extremely expensive and charged in
3-minute units. Few people wanted to prolong a call once they'd heard
"the pips".
--
"Mrs Redboots"
http://www.amsmyth.demon.co.uk/
Website updated 18 December 2004