I haven't had the 'joy' of a First school Christmas performance for years, but still remember the phones being held up and the talking, 
I used to find the whole thing quite stressful. Never got a seat with a decent view and the same parents always seemed to get the front row and seemed to have the whole extended family with them rather than just the 2 tickets allowed.
One performance DS1 accused me of not being there, because he just couldn't see me.