Re: Does anyone remember this payphone trick? [Telecom]

The most common pay phones, until the 1970s, were "ground start". What

> this meant was that the phone was de-energized, so to speak, and > there was no dial tone in it, until... > > ... until the "hot" wire in the phone cable was shorted to ground. > > This signalled the central office to activate the wires and > send a dial tone across. > > The official way this occurred was when the pay phone detected > a coin falling through it and toggled an electrical switch.

In rural areas there was a dial-tone-first "post pay" design that worked a bit differently. One listened for dial tone then dialed the number. Upon actually reaching the desired party (not a busy or no answer), one would then put in a dime or two nickels to allow the transmitter to function. These pay phones were simpler all way around--the phone was simpler since it didn't have a deposit holder-- the coins just dropped straight through. The CO gear was simpler, too.

As an aside I noticed that all the payphones in my village have been removed; the last ones in front of the convenience store were just pulled out.

At one time a few square blocks of the village center had pay phone at:

1) In front of convenience store (pair). 2) in front of the drugstore (booth) 3) in front of pizza shop 4) inside lobby of bar 5) outside of bar 6) inside nice restaurant 7) semi-public inside coffeeshop.

One pay phone remains at the train station, but I think it is essentially subsidized by the railroad to serve as an emergency telephone. It appears various railroads are doing that. The phone co will install a payphone anywhere, but the property owner must guarantee a minimum revenue or they must make up the difference. I would guess that the cost of a stardard public pay phone is less than the cost of a dedicated 'lift-receiver for help' phone directly connected to a 911 center, and of course more flexible for public use.

Not everyone, even today, has a cellphone, and even for those that do the batteries run out, the phones get lost, the pay-as-you-go contract is not kept up, etc.

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I did this in the late 80's early 90's at my junior high to get picked up from sports after school. Paper Clip in center hole of the phones mouth piece and there was a tiny indent on the metal of the old pay phone. Must of been an older pay phone. Worked every single time I needed it.

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In the college dorm in the 50s there was a wire with a nail on the end ran from the water cooler to the pay phone area. To get a dial tone just poke it through the hole in the center of the handset mouthpiece. The hole was worn from much use.

***** Moderator's Note *****

At certain colleges, during the 1960's, there was a special use of the Vice-President's name:

Spiro -> Blue Box T. -> Bridged "T" Rectifier Agnew -> Black Box

The "T" in the above list was used to modify a payphone connection so that the 'coin collect' battery would arrive at the pay phone as 'coin return' polarity. It was obviated by the fraud-latch in the 'Fortress' phones which replaced the 200 series.

Bill Horne Moderator

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I found a genuine working pay phone. It is at a swimming pool, and apparently they pay for it to be available as a backup emergency phone.

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Never heard of that. I worked at SBC for 35 years (till 2003) [as an] outside cable splicer [doing] installer/exchange repair [and] finally [as a] comm tech special circuit tester.

The old 333/335 had the relay isolated from [the] chassis. The relay got trigger from the CO to setup loop once coin was dropped. I remember testing all relays with [a] testcenter tester as he sent proper volts/amp ([I] don't remember which) to the relay to trip and release. We had to [do] all line test/relay tests, and made sure we had a good ground when we installed or repaired all coin phones on our service orders or tickets.

Later, these phones were replaced by the 1A and 1C [types, which were] all Western Electric coin phones which had "dial tone [first]" service and then people tried to hack them using "blue boxes" for LD calls. Most of [the] US coin phones are now in other countries or [were] sold as home conversation pieces: I was lucky and have several 333's and an old wood pay phone booth complete.

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I never saw anyone using a bobby pin to get dial tone, but it was technically possible, at least for very early types of "3 slot" payphones. There's a scene in the movie "War Games" where the protagonist removes the microphone cover on the handset and uses a soft-drink-can tab to ground one of the leads, thus getting dial tone. As with most Hollywood portrayals of phone hacks, I doubt that was possible in any actual payphone: when I started working on them about five years ago, and all the mouthpiece covers were glued on.

Dial-tone-first payphones routed all "0 plus" calls directly to a TSPS tandem in the New England Telephone service area, and I don't know if the trunks that connected them with local offices were supervised with SF signalling, which would be required for a blue box to work. I'd bet that the "pheepers" whom were using blue boxes had to dial an 800 number to get away from the TSPS system and onto an SF-supervised trunk in order to use the blue box.

At M.I.T. in the late 60's(1), there were code words for most of the hacker methods, e.g., a "Spiro" was a blue box, a "T" was a bridged-T rectifier(2), and an "Agnew" was a black box. I never heard of a code word that meant "grounding a ground-start dial tone line by putting a pin in the microphone of a payphone," but that's not proof that it wasn't done.


  1. Full disclosure: I wasn't enrooled at M.I.T.: I worked at the student run radio station, learing the profession that supported me for about five years. My degree is from Northeastern University.

  1. A bridged-T rectifier could be inserted in the cable connection of a 3-slot phone, in order to change the coin-collect voltage into a coin-return voltage. Single-slot "Fortress" phones had a "fraud latch" that would diasable the phone if a "T" was used, requiring a field visit to reset the phone.

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Indeed it worked, pre-9-1-1 time. Pay phones were basically ground-start lines with the ground completed via the coin relay and a switch that closed when a coin was deposited. No ground on the coin relay, no dial tone, no free calls. This arrangement also allowed the C.O. to apply a voltage of alternate polarity to ground in order to collect or return coins.

The "War Games" trick worked before they glued the handset caps on. Similarly, a pin through the handset cord to ground would accomplish the same thing.

After armored cords and glued caps became a thing, one could insert a pin through one of the holes in the transmitter cover of the handset. The T1 transmitter elements contained a metal diaphragm that was electrically connected to the carbon cup. Grounding this got you dial tone. It also eventually damaged the transmitter.

The last battle in that war of which I'm aware was a special pay phone transmitter that had an armored steel cover insulated from the circuit instead of the plastic perforated cover on the T1. The metal cover was crimped in such a way that it had perforations perpendicular to the cover. Sound would pass but you couldn't get a pin through.

To the best of my knowledge a ground would allow free calls on either three-slot or one-slot pay phones as long as the central office was configured for traditional ground-start payphone lines.

Somewhat later there was a mandate to allow emergency calls without coins. In addition, Bell wanted 800-number calls to be dialable without coins as they were a cash cow.

The CO equipment was modified for loop-start, so dial-tone-first. Emergency calls, service numbers (including 4-1-1 which was a free call back then) and 800 numbers would complete automatically.

A coin in the hopper would still provide a ground through the coin relay, so no modifications were needed in the paystations. If no ground was present, CO equipment would intercept local calls and play a recording, "The call you are making requires a coin deposit. Please hang up, insert coin, and place your call again." Toll calls would route to operator.

Later, after the three-slot phones with the bells and gong were all replaced with single-slot, toll calls could be automated by counting the tones from the oscillator. Enter the red box that would emulate the tones of the coin totalizer.

After dial-tone-first, high school kids short of lunch money would find the ground connection on the campus pay phone and lift it. Victims would hear dial tone, put their dime in, and try their call which would fail. Because of the lack of ground, the coins would remain in the hopper as there would be no connection to the coin relay. Later, the kids would re-connect the ground, pick up the handset, yell "Jackpot!" and hang up. The CO would detect an incomplete call and return all the coins.

***** Moderator's Note *****

The coin-collect and coin-return battery voltages were applied between tip and ground AFAIK: +130 for coin collect, and -130 for coin return.

The current crop of COCOT phones have computers in them, with ~4 volt batteries that are trickle-charged from the CO line voltage. The onboard computer does all the tasks which used to be performed by the CO's equipment: rating calls, collecting or returning coins, etc., thus allowing customer-owned payphones to be used with standard 1MB dialtone.

Bill Horne Moderator

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Jay Hennigan

Technically, the dial tone provided by a COCOT is not from the CO. The COCOT plays its own dial tone and completes the call once a number is dialed. COCOTs don't let you get at the CO dial tone. You can hear the DTMF digits in the background once you've dialed the number and inserted the proper deposit. 0 and star numbers are also programmed to toll-free numbers. The COCOT itself is programmed to call home to the payphone provider every couple of days or so.

There are a number of ways I've discovered in the past few years that make it possible to phreak COCOTs, too, particularly PTS ones, but they're not nearly as exciting as the old ways.

I'm currently putting the finishing touches on virtual coin trunks for coin-first, post-pay (WECo and AE) and dial-tone first pre-pay operation. Surprised by how well they work, but also appreciative of just how many moving components there are with real trunks and how they operate together!

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Naveen Albert

Another strange thing about many COCOTs is that the DTMF digits played to the handset were scrambled while making the call. They sound like real DTMF tones, but the digits heard in the handset don't match the digits dialed. Calls completed as expected, but the audible feedback was rather confusing espeically when calling a familiar number.

Do you know why this was done? I can't think of a valid reason.

Once the call completed, the actual dialed digits would be played both over the line and through the handset. Things like voicemail, IVR, etc worked as expected.

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Jay Hennigan

I did this too- but in 1984 in Milan, Italy. I had always thought it was an Italian thing. LOL. Soon the police caught on and we didn't do it anymore.

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