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.