It’s not clear exactly when the hotline started, or by whom, but it was probably sometime in 1981 when Swedish teenagers discovered they could hack Televerket, the monopolistic state-run telecommunications company that ran the national phone service. When a phone subscriber moved addresses or just ended a subscription, Televerket allowed the old number to remain out of use for a while so when a new subscriber was given that number, they wouldn’t have to deal with calls meant for the previous subscriber. During that interim period, when someone called the unassigned number, they’d hear a recorded message — something like “please dial 90120 for information” — followed by four beeps. The message would repeat automatically, but there would be a silent gap between them.

Somehow, someone figured out that if you called one of these unassigned numbers — or one of a series of connected unassigned numbers, maybe from a disbanded company with multiple lines — at the same time as someone else, they could speak to each other during the gaps between the automated messages. At the time, most calls were charged per minute, but these calls to unassigned lines were free. So you could speak with friends, or strangers, for hours. And it wasn’t limited to two people. Some of the numbers could accommodate up dozens of callers at once.

Once discovered, wrote Enzensberger, “The numbers spread through the Stockholm schools like wildfire, and an enormous, spontaneous conference circuit came into being, a new mass medium: the ‘hot line.’ It’s hardly possible to use modern communications technology more intelligently.” An article in an internal magazine published by Televerket said, “The youth have shown an unparalleled resourcefulness.”

“I wanted to meet new people and tried to get away from that small town I grew up in. That was probably one of the main reasons I got into the hotline.”

The hotline was made possible by a design flaw that emerged as the phone system was in a transition period between electromagnetic and digital technology, according to Ralph Arnestig, who was head of customer relations at Televerket in 1982. When a line turned from active to vacant, a single number could accommodate two to five callers at once. They callers weren’t meant to hear each other, only the automated message. But since each caller connected to the same transformer, they could also hear each other. Arnestig said groups of vacant numbers that belonged to a private branch exchange, or PBX — an internal phone system that might be used by a private company, for example — could accommodate as many as 49 people at once.

With that many people trying to speak over each other, it could be a bit messy. You had to shout if you wanted anyone to hear you. “It was everybody going, ‘Hello, hello, hello, hello,’” Patrik Olofsson said. “It was crazy.” When Olfosson was 15 and living in the small town of Finspång, about 100 miles west of Stockholm, he was obsessed with the heta linjen. He said it was like a drug for him. Every day after school, he’d head directly home, get on the phone, and stay there for hours, talking to teenagers living outside his industrial town. I asked him what he spoke about, and his answer basically described my (and most people’s) time spent on the internet. “About everything,” he said. “Nothing, and everything.”

One of the people Olofsson met on the hotline was Carina Hilmersson, now an accountant living in Stockholm. When she was 15, Hilmersson would get together with her friends and call the hotline together. She kept long lists of hotline numbers, which were constantly changing when lines became too busy with callers or when Televerket put a number back into official use. “Every time you got on the line, you got more tips,” she said. “Someone told you about another number you could call to get to know more people.”

Olle Lindgren, who hails from the island town of Vaxholm, said he spent a lot of time searching for new numbers. “Some of the lines were very noisy. It was extremely difficult to pick out a particular person from the multitude,” he told me. “It sounded like if you walk into a really busy party and try to talk to someone across the room.” The recurring automated recording was louder on some numbers than others. Hotliners would search for numbers where the message was softer and easier to speak above to be heard by the other callers.

“Eventually, you got into a ‘club,’ if you like, where you had access to numbers where not many people dialed in, and you started to get to know people,” Lindgren said. When a line got too busy, you’d tell your hotline friends, “We’re switching,” and then give the nickname of the new line, which only insiders knew. Then you could talk in a more private setting. Lindgren kept a small phone book with the most common numbers. But the numbers you used often, he said, “you knew them by heart.”

Lindgren spent a lot of time searching for new hotline numbers. He said old company lines were the best, because they would usually include a whole series of connected numbers. “You tried to find how far the series of numbers went,” he said, describing the process. “You start with something ending in 00, and then you went 01, 02, 03, and eventually you could hear that it was a different kind of answering machine or the sound was higher or lower. So you knew that you were out of the rain. You could get a range of 10 to 20 phone numbers and start handing those out to friends and hopefully get a line started.”

But searching for new numbers was time consuming, because in 1982, most people had rotary phones with slow circular dials. Every time you dialed a digit, you had to wait for the dial to slowly work its way back before dialing the next one. Lindgren took his phone apart and trimmed a spring so the dial would roll back quicker. Regular landline telephones then didn’t have a speakerphone option, either, so Lindgren and a friend connected a radio transmitter to the phone so he could listen to the hotline on the radio and even record conversations. (Sadly, he no longer has the tapes.)

When she first started calling the hotline, Carina Hilmersson kept it a secret from her parents, but soon she had to fess up when the line was always busy and nobody could ever call the house. Eventually, her mother got used to it. One day, she didn’t know where her daughter was, so she called a hotline number that Hilmersson had written down, and asked for “Cina,” her daughter’s hotline nickname. Hilmersson was at a friend’s house—on the hotline, of course—and her mother found her and told her to go home. “I was so shocked and embarrassed,” Hilmersson said.

Like today’s social networks, and the internet in general, the hotline offered a chance to connect to groups of people outside your immediate physical space. With all these teenagers speaking via the hotline, it only made sense that they would eventually want to get together in person. Rålambshovsparken was not the first time people from the hotline had gotten together. Olle Lindgren from Vaxholm said he would learn about parties in Stockholm through the hotline. He’d call in late during the school week to make plans for meeting at a certain place and time on the weekend, sometimes for small gatherings, sometimes for big. And in this magical time of landlines, you had to plan in advance. “We were kids—we wanted to meet, we wanted to hang out,” he said. “Rumors got along that someone’s parents were out of town, so there would be a party at the house. Everybody went there. It was just kids having fun.”