Whoa! That takes me back to the mid-60’s when we found a way of getting free calls from ‘phone boxes.

By tapping out the number on the bar on the telephone cradle you could get connected for free. You had to tap the number with a pause between numbers and the numbers ‘0’ and ‘9’ could be dialled.

Does that ring any bells? – although it used to ring a few numbers!

We didn’t think ourselves as ‘phreaks’ though.

Hugh                                                                                                      Amadeal Ltd

Old phone boxes used to have a coin mech that generated 10pps “dial pulses” to indicate the coin type.  In order to discriminate between these and normal pulses the line was reversed in “quiescent” mode and series diodes used in the payphone to decide which of the dial or mech was in circuit.  Once a valid coin had been signalled the exchange would reverse the line back to normal to permit dialling and speech.  I knew of at least one payphone in a university hall of residence where enterprising engineers had shorted out the dial diode so the coin value could be “dialed in”.  Ah, those were the days before hacking became a thing.  I recall that Plessey had a “consulting vandal” they used to try to break payphones too.

On 20 August 2025 at 09:54 Hugh Stewart-Smith 1 Said:

Whoa! That takes me back to the mid-60’s when we found a way of getting free calls from ‘phone boxes.

By tapping out the number on the bar on the telephone cradle you could get connected for free. You had to tap the number with a pause between numbers and the numbers ‘0’ and ‘9’ could be dialled.

Does that ring any bells? – although it used to ring a few numbers!

We didn’t think ourselves as ‘phreaks’ though.

Hugh                                                                                                      Amadeal Ltd

Yes, I remember that from my university days in the sixties.  You could also make long distance calls by stringing together dialing codes to get from one exchange to another.  If you went through too many exchanges to reach your destination the call quality became only just intelligible.  The exchanges used electro-mechanical switches called uniselectors which advanced one step for each pulse you sent.

Russell

The other game was to string together a load of dialling codes to ring the phone at the neighbouring desk in the same office.  “We made our own entertainment in those days…”

Phone freaking was a little more advanced than just cradle tapping which was used to make free local calls from phone boxes connected to strowger exchanges. So for instance the whole of London was on one network of linked exchanges so a call could be made from say a phone box in south London and phone in say north London. However before trunk dialling was introduced long distance calls had to be made using an operator. However there was a way from a phone box to unhook from the local exchange and link across onto the trunk links between exchanges. If you knew the code numbers of the exchange you wanted to route through you could act like “the operator” and route you call yourself. When automated trunk dialing was introduced routing to and through exchanges was done using inband tones and again if you knew the tone sequences that identified the exchanges one could route ones call anywhere on the network. I believe Steve Wozniak was an early master of phone freaking in the State and look where that got him.

Clive S

I had a friend who back in the 50/60’s had a business in Farnham Surrey and a flat in London. All his business calls from Farnham were long distance and mainly to London which was both expensive and you often had to book a call or the operator would call you back. I don’t think the bottleneck was the number of circuits between Farnham and London but the number of operators. Anyway being technically minded about telephones and the network he rented from PO telephones a long distance DC line from Farnham to his flat which you could do in those days. He then designed and installed, in his flat, a relay based unit to link from the DC line to the London telephone network so he could dial directly from Farnham to anywhere in the London telephone area. He continued to study the workings of the UK telephone network from information freely available at the time and could see where various improvements could be made so approached PO telephones with an offer to act as a consultant. They declined his offer saying they didn’t need such a service as their guys knew better. Anyway he went on to use this knowledge to enable him to not just link to the London area phone network but also to link into the Tandem network that linked exchanges countrywide. Eventually PO telephones cottoned on to what he was doing and decided to prosecute him. He recorded all the calls he made and his defence was that he never intended to defraud PO. Unfortunately his business partner wasn’t as diligent and didn’t record his call and this was his undoing. I think the case was heard in the High Court and PO went to great lengths and expense to show the jury how he did it. He was found guilty of “stealing PO electricity” and fine £1000 but PO want their costs which was much more. However the judge ruled that he didn’t deny the “crime” so their explanation was unnecessary so no costs were awarded. Even so a £1000 then could buy a very nice house but his flat was in Pimlico so he was exactly short of money. He thought he was the first Phone Phreaker.

Clive S

The UK did move to tone signalling IIRC as pulse was far too slow as traffic volumes increased. It would surely have been different to the rest of world to “protect our home manufacturers”. That went well didn’t it? All became obsolete when digital transmission and switching took over.

Mildly off from the original topic (but, hey, it’s the forum….), I worked for a company selling indoor payphones in the 1990s.

These used a series of ramps that the coins ran down at a known velocity taking them past 2 or 3 coils, thus generating a repeatable signature depending on the metallurgical make up of the coin. Once a sample of a few hundred coins had been tested, the thresholds for each coin value were defined and the payphones shipped where they ended up in bars and hotels primarily.

However we shipped some 20,000 units to Spain and suddenly started to get feedback that a rather smaller coin was being mis read for the high value 2 Peseta – to the extent that some machines were stuffed full of the low value coins and the ultimate telephone bill ran into the thousands….
Turned out that some “ladies of the night” were passing the time between clients by getting a biiiig bag of the low value coins from the bank and putting them through the payphones which instantly displayed the coin value on the screen and then the coin reject button was pressed. Every coin that showed a 2 Peseta value was placed in a different pile…and were subsequently sold on as “international calling tokens”….

We had no small effort involved to update the payphones in the field to eliminate the issue.