Cheat on your boyfriend if you must. But don't share it on speakerphone with the rest of us

Smartphone noise pollution is altering public spaces, so why are so many of us guilty of it? Kate Maltby takes to the street to find out

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The young woman on the train seat behind me returns my gaze and widens her eyes in amazement. She is, as I have learned in excruciating detail throughout the journey from Purley, south London to London Bridge, a trainee nurse - early 20s, active in her Pentecostal church - all dressed up for a big night on the town. Tonight she hopes to cheat on her on-off boyfriend in revenge for him lying about his continued intimacy with the mother of his child.

Thanks to the volume of her call, which is set to speakerphone, with graphic interjections from her friend on the other end, we have heard it all. I gently ask why she is not using headphones for a private call. She is not hostile, but is stunned that I would ask the question. "But nobody I actually know is in this carriage," she explains. "They can't hear me."

Nothing in the past 25 years has altered our public spaces like the auditory pollution of the smartphone. The arrival of the boom box in the US in the late 1970s offered a glimpse of a future of portable music, but those who dared to pump beats in public spaces often found themselves at the centre of a clash of cultures.

In films, heroes were applauded for inflicting violence on them. In a famous scene from the 1986 movie Star Trek IV: The Voyage Home, a time-travelling Mr Spock and Captain Kirk find themselves on a bus in San Francisco, where they are shocked by the audacity of a punk blasting out a track from a fictional band, aptly named the Edge of Etiquette. Spock cements his status as everyone's favourite alien-human by using his Vulcan nerve-pinch to render the offender unconscious. Onlookers cheer.