I carry a mobile phone for work. No, I'm not some high mucky-muck. I spend a lot of my day away from my desk but have to be contactable. A mobile phone makes perfect sense, in this case. I make very few calls on it, preferring to wait until I get back to my desk and relative privacy.
I've noticed that for a lot of mobile users, their voice volume increases according to the inappropriatness of where they are when making a call.
Cheers,
Maso