Wired has the umpteeth article on how to be polite with your cell phone, covering all the stuff that anyone with common sense should be able to figure out without this article, and some of which I wrote myself almost ten years ago.
I have to disagree with one point, though: "Don't talk on the phone while you're grocery shopping. For whatever reason, the acoustics of a shopping aisle seem to amplify your voice. Also, talking on the phone tends to distract you from what's going on in your immediate vicinity and I need to get around you to reach the Cocoa Puffs."
Buzzzzt. Sorry, wrong answer. Being able to call and verify the items you may have forgotten and thus save an extra trip to the store is the single most useful experience of owning a cell phone, aside from calling in a vehicle emergency.
I'll agree with you that far, but other than that use, please don't. I still can't get over people talking on those things in public about topics I'd rather not know anything about.