I can't believe the numbers of young people I see walking down our street having loud conversations on their mobiles. For me using a mobile is slightly embarrassing so I do it furtively, somewhere I can't be overheard. I certainly don't use my phone when I'm having dinner or a meeting with somebody, that's the height of rudeness.
I once sat on a train to London opposite a woman who went through her entire address book telephoning people and telling them "I'M ON THE TRAIN...." very loudly. Since I was obliged to listen in to each call, I quickly realised that she wasn't calling for any particular reason, she just wanted everybody to know she was on the train to London and using a mobile phone. Muppet.