"I never hear my phone", I remarked, as I noticed that I had missed a call at about 7pm. "Oh, that was me", said one chap, "I phoned from the corner of the street, but then I realised I was not lost after all." "Oh, that's because you have it set to DO NOT DISTURB", said someone else, "See!" "Oh, I see", I said, though I didn't really see at all. "And I never hear it when Alan sends me a text message", said Pat. "Oh, look, you have it set for do not disturb for him - oh yes, and for me" observed Catrin. Honestly, it's like teaching your grandmother to use a spreadsheet.