The matter of etiquette is Biblical, of course, as we may be reminded by the Apostle Paul: "Be kindly affectioned one to another with brotherly love; in honour preferring one another" (Romans 12:10). This matter must apply also, in the 21st century, to the use of cellphones.
An interestting article in today's Wall Street Journal got me thinking about the phenomenon of everyone on his cellphone in the midst of daily commerce. It's not necessarily a bad thing; and in some ways it serves to connect people, which is a good thing. It's simply important to remember that as various societal customs and interactions evolve, the question of basic decency and courtesy should not.
People who use cellphones (that would be most of us) should remember, for instance, not to break off one conversation to engage another in midstream. This has always been true, of course; now it must be applied to cellphones. When in a crowd, if you are in the midst of conversation with one person and another approaches you, that person should wait his turn at a discreet distance, of course; but if he should forget to do so, the appropriate etiquette you is somehow politely to ignore him for the moment or, if necessary, subtly bid him to wait a moment. The same should apply to cellphones.
Thus if you are in conversation with someone and your cellphone goes off, it is appropriate to ignore it, or better, to act quickly to silence it (if it frequently goes off, perhaps it should be on vibrate at all times).
Simply put, it is rude to break off a live conversation to answer a cell call or text.
And of course, cell phone conversations, or texting, should be right out, during dinnertime.
We should be teaching this to our children, along with all the basic rules of etiquette, when we can.