"This persons list of rude things starts with cellular telephone use, as if talking on your cell phone in public is the rudest thing you can do. I do not agree. Talking loud, whether to your companion OR on your cell phone can be distracting to those around you but it is not nearly #1 in rudeness. I find any of the other things listed to be more rude than a cell phone conversation. Not turning your cell phone off in church or movies IS bad and allowing it to ring there should NEVER happen."
True, and I agree that there are times when cell phones should always be off, like the example you gave. However, there are some "cell-phone-nazis" out there where if they can hear you talk on your cell phone at all they act like you just walked up and slapped them across the face. (not saying that's here on FR, but they're out there) Granted, it's annoying to hear someone gabbing loudly on the cell phone, but still it's a convenience we have because we want the flexibilty.
For example, if my girlfriend sends me to the store for some item, I am standing in the aisle where that item is stocked, and I make a call from there with a question about what type/flavor/color I should get, or if I call home from inside the store to ask "rice or mashed potatoes with dinner?", etc.. get over it! I'll keep it short if I can, you're not gonna die.
This is why we have cell phones, it's tremendous convenience. Just wait until your car breaks down on the side of the road without one.