My mum has one, turns it on to call me, or to leave me a voicemail then turns it off.
She cannot understand why this drives me to the very edge of my sanity...
there's an even better reaction when you use that line on the boss:
Him - why do you have a mobile phone when you don't answer it?
Me - do you mean last Friday? The last day of my holiday? When I was driving back from Plymouth?(this was 22 years ago, so hands free in my 19 year old Capri wasn't really feasible) I'll deal with the problem now.
Him - but we did that on Friday!
Me - so you didn't need to speak to me at all. Like most of the phone conversations that happen here. I pay for it, for
my convenience.
Him - stomped off muttering, and avoided me for nearly a week
One of the benefits of modern phones showing who is calling is being able to filter the conversations you don't need or want to have. Although that usually leads to a load of texts you also have to ignore.