Quite right too.
I'm sure the business of running the country is more important than whatever might justify a mobile phone going off in a Cabinet meeting. If World War III is declared I'm sure someone will interrupt to let them know.
There's nothing more annoying than being in a meeting or having a discussion when you get interrupted by a mobile phone going off.
Not only is it polite to switch off your mobile while in a meeting but it shows that you respect the other person or people that you're with and you're paying attention to them and not being distracted by something else. Your priority and your attention should be the person in front of you.
Get into the habit of switching your mobile off or to silent mode when you go into a meeting. If you're running a meeting make sure you ask people to switch off their mobiles at the start of the meeting.
If you really are expecting an urgent call, let the person know that you may be interrupted and that you'll need to take the call but you can still turn the volume down or set it to vibrate.
There's a time and place for mobiles - don't let them take over.