It's easy to be rude with a cell phone. A visitor from another planet might conclude that rudeness is a cell phone's main purpose. Random, annoying ring tones go off unexpectedly. People talk too loudly on cell phones in public because of the challenge of holding a conversation in a noisy environment with someone who's not present. Cell phones need their own rules of etiquette, or we'll descend into social barbarism.

But cell phones -- and the ways we use them -- change. In the past three years, the whole world of cell phones has evolved so much that we need some additional rules of etiquette.

Of course, all of these old rules for the courteous use of a cell phone still apply:

* 1. Lower your voice when taking calls in public.

* 2. Avoid personal topics when others can hear you.