That's why I have a mobile phone. Because I am on call 7 days a week, 24 hours a day. I'm not working all that time - if I was working I would be in the office, not in the cinema. Sometimes I'm in bed - but the mobile is still switched on. We have a contract with our customers that they can call us for support (not development - if I'm not in the office I'm not able to modify programs) 24 hours a day, 7 days a week. Only day they can't call us is Christmas Day, and that's cos they don't work Christmas Day either. Actually, they do have a skeleton staff even on Christmas Day, but they shouldn't need to call us as they don't use the software we have written for them on Christmas Day.
I don't expect the phone to ring (vibrate) - it happens maybe once or twice a month outside office hours Monday to Friday. But, because our customers pay us rather a large sum of money every month for the security of being able to call us outside office hours, we would be breaking the terms of that contract to not allow the customers to call us. It's no big deal - many companies offer the same service. My girlfriend always has to have her mobile switched on also - because she is the first port of call for all the engineers who work for her if they have an emergency, and they are working from 4 in the morning until midnight.
That doesn't mean she is permanently getting these calls at 4 in the morning, it just means that she has to be available if the calls come through.
My mobile is paid for by the company I work for - one of the conditions of having that mobile is that it is always switched on and I am always contactable. I'm not going to not go to the cinema just because there is a chance that my mobile will call me away - the chances are that it won't call me away. And even if it does, the money that we make for having this contract means that I can afford to go to the cinema again the following night and watch the film from where I missed it the previous night - if I wanted to.
You seem to be under the impression that I am only contactable by my mobile when I am working - wrong! The mobile is to ensure that I am contactable when I am not working. When I am working you don't need to call me on my mobile - you can get me on my office phone. Therefore, the only time you would call me on my mobile is on my days off - the eminently more sensible time to go to the cinema.