Kevin McDonaldJun 18, 2025

Long before the internet, some phone networks were hackable by playing a single tone at 2600Hz.

Whistled into a phone, it could grant you unrestricted access. Do you have the vocal chops to be an old-school phone phreak?

I built a web app to test your ability to produce the legendary frequency. You won't get free long distance calls but you will get some honor in the knowledge that you could have been a cool hacker. 😎

I am sad to say that I can only whistle up to 1100Hz... But my wife (a long time woodwind player) is able to consistently get it.

Give it a try: https://phreak.kmcd.dev/

#phreaking #2600Hz #bluebox #RetroComputing #hacker #infosec #Tech

Phone Phreak Emulator

Test your phreaking skills by hacking this phone line.

Show threadIan K TindaleJun 18, 2025
@sudorandom when was this ever true? The earliest phones I remember in the 1960s used carbon microphones but had no awareness of tones anywhere in the system, at least from the GPO phone in the hallway by the door. You could dial by imitating clicks by pressing the hook in and out several times, but there was absolutely nothing to do with tones about a phone.
Show threadlpbkdotnetJun 18, 2025

@u0421793 @sudorandom 2600Hz signalling was mostly in use in the USA.

In the U.K. trunk lines between exchanges often used 2280Hz signalling to route the call.

You would often hear a chirp at the start or end of a long distance call

Eg you can hear the chirp at the beginning of this Noel Edmund’s phone prank:

https://m.youtube.com/watch?v=5ptcKL_T1xw

You may be able to hear another at the end, I didn’t get that far!

More info than you ever wanted about uk telephone signalling here:
https://www.britishtelephones.com/pwover1.htm

Noel Edmonds Phone Calls - Haggis Shooting

YouTube
Show threadlpbkdotnet

@u0421793 @sudorandom if you want to see a live demonstration of 2280Hz signalling, visit Milton Keynes Museum.

They have an interactive demo (using real GPO equipment) that allows you to listen in on the trunk and hear the beeps that were usually hidden from callers.

It’s an excellent museum with a lot to see and do!

It’s a bit trickier to whistle off a 2280Hz trunk, than it was in the USA, but it was absolutely possible in the UK.

Source: I’ve done it

Jun 18, 2025 at 12:26pmWeb
Show threadAlex@rtnVFRmedia Suffolk UKJun 18, 2025

@lpbkdotnet @u0421793 @sudorandom there was also a *lot* more official secrecy about the British telephone network and it was harder to get any information about it until well into the late 1990s. There were also filters in some cases to prevent 2280 Hz being sent down the line from the subscribers end, and even alarms that sounded if it was detected. Phone phreaking was considered fraud against the public purse so risked heavy punishment.

By late 90s it was possible to bluebox some Global Majority countries via Country direct (dial 0800 89nnnnn and send 2280/2600 tone down when you heard the pip) but I never did it as it didn't seem ethically right when you could already legitimately get dirt cheap phone calls compared to the 80s/90s...

Show threadlpbkdotnetJun 18, 2025

@vfrmedia @u0421793 @sudorandom "harder to get any information about it until well into the late 1990s"

The city & guilds textbooks Telephony by Herbert & Proctor (1938) and Atkinson (1950) both describe VF signalling in detail. The POEEJ was available in libraries.

Toll-A Dropback was exploited in the 50s, trunk stacking and payphone dodges go back even further. New Scientist wrote about it in Dec 1973!

The filters, alarms and split signalling did make it harder, but not impossible....

Show threadlpbkdotnetJun 18, 2025

@vfrmedia @u0421793 @sudorandom The key difference between the UK and the USA wasn't so much technical as it was sociatal.

US phreaking became very counter-culture, "stick it to the man, free long distance for everyone!" with celebrities buying blue boxes.

In the UK, it was far more "interested geeks poking at it for fun to see what it did" with a sense of fair play.

Well, except for those phone engineers inside the system who were abusing their position... but that's a whole other story!

Show threadAlex@rtnVFRmedia Suffolk UKJun 18, 2025

@lpbkdotnet @u0421793 @sudorandom

I read Atkinson in the 1980s (had to get it from the library) but only knew about it as I'd been tipped off by engineers at the BBC Receiving Station in Crowsley Park who told me and my friends how the telephone network worked (the BBC and BT operated closely together in that area as BBC Monitoring had HF receivers that could be remotely controlled over the telephone network like todays SDRs)

Show threadlpbkdotnetJun 18, 2025

@vfrmedia @u0421793 @sudorandom Atkinson is amazing! I regularly refer to my copy! I may be an outlier... 🤣

The UK phreaking stuff is a favourite subject of mine (can you tell?) and I've spent a lot of time talking to a couple of the 18 people tried at the old bailey in the 1973 "telephone trial of the century" as it was reported in the national press.

They have so many fascinating stories to tell, but not all of them are proud of their past adventures.

Show threadDan PiponiJan 14
@lpbkdotnet @vfrmedia @u0421793 @sudorandom I believe one of my school teachers was one of those 18. AFAIK he was found not guilty.