I agree with Marje. It irritates me no end to see people sitting there Facebooking, texting etc while someone else is singing, plainly not giving the singer even a fraction of their attention (have just made same point on the other thread). It is just plain rude, and I'm becoming a GOW.
If people must have their phones visible to receive important messages, including bus times, family emergencies etc, then if the phone does go off (silently please) move away to answer it, as Marje also suggested.