On the 900 bus a trio of females – mother, two daughters – occupy three rows, two seats apiece. Each of them has a mobile, each with its own ringtone – George Michael’s Careless Whispers the winner in the irony stakes. The younger of the two sisters gets a call – her ringtone some generic electro racket. Hullo? She listens. Who’s this? she asks. She listens some more. Unsure but assertive, she speaks up. Who is this? Alerted, Big…