to answer or not... to hang up the phone.. or not

I took a class for work last week on customer service and one interesting conversation ensued... We were talking about using cell phones while shopping, driving thru a restaurant, etc. People have serious opinions about that.... In fact several found that it was really rude to talk on the phone in a store or basically anywhere in public. I as curious... if I am driving thru to get a diet coke do I need to stop talking on the phone to pay my 1.50 and then get my soda, or if the phone rings, its your child's school do you pick it up when you are checking out or wait and call them back? I was in an office supply store checking out, my phone rang and I chose not to answer it, the clerk thanked me commenting it was rude to have answered.

I am so curious what you all think.. please chime,. I will comment tomorrow nite.