It's a familiar call at the start of any conference: switch off your mobile or at least put it in silent. But does anyone ever bother? A survey by a UK conference centre suggests not: 75% of attendees left their phones on regardless of requests, and of that group, 40% check their email at least once every half an hour. I know I'm guilty of doing that. Is it now acceptable to check your email or phone during a conference, or do I need to get better manners?