On Sat, 24 Jun 2017 10:18:34 +0100, "dennis@home"
wrote:

On 23/06/2017 23:44, Steve Walker wrote:
On 23/06/2017 09:09, wrote:
On Friday, 23 June 2017 00:49:11 UTC+1, Steve Walker wrote:
I think it was only in the '80s that they changed the tone received by
an operator from a payphone - until then they could not tell them from
private phones and people had learned that you could make free reverse
charges calls *to* phoneboxes.

This was because the 1980s GPO/BT owned all the payphones and knew
which lines were coinbox lines. It was possible to make reverse charge
calls to a payphone because the operator could ask the person at the
payphone to insert money to pay for the call (and on the old Button
A/B boxes listen to the separate 'dings' for sixpences and shillings).

When private payphones were introduced they were connected to ordinary
lines so the operators had to have some means of knowing a payphone
was connected, hence the 'cuckoo' tone.

Owain

Well BT didn't use their knowledge well, as people were making such
calls without the operators catching on from what I remember

SteveW

It wasn't BT's problem, they just billed the calls to the line renter.
The renter could have incoming calls blocked if it was a problem.

That's correct, BT had no incentive not to bill the user for these
calls, remember when implemented, the payphone itself generated the
cuckoo tones when any of the allowed operator codes 1xx was dialled.

I actually discovered an exploit on the Landis+Gyr Agifon 50, and I
even brought it to the attention of the manufactures.
It had to have the original old firmware
The phone had to be set up for LD dialling

As I recall it went like this, the hookswitch was reasonably protected
with a delay so you couldn't "tap-dial" but in some exchanges with a
little practice you could use the hookswitch to dial a single "1"
you then dialled 0072 on the keypad normally.

The *exchange* would see 10072 which would of course connect you with
the operator (the 72 would be ignored of course).
The *phone* however would think 0072 had been dialled and that was at
one time a prefix for a toll free radipaging service, and the phones
firmware treated it the same as 0800 0500 0808, so no cuckoo tone!


--

Graham.
%Profound_observation%