The New York Times had an article the other day on electronic gadgetry etiquette.

I have my own code of etiquette that I try to follow when it comes to picking up phone calls and texting.

• If you are hanging out one-on-one with somebody, it is rude to pick up a phone call and hold an extended conversation, unless it is an emergency. There are some situations where it might be acceptable to pick up the phone, for example, if you're meeting up with another friend and need to give them directions or tell them you're running late. Otherwise, you should give your real-life friend your time and attention. I was once driving to the mall with a friend who picked up a phone call and proceeded to have a 25-minute conversation with another friend. I found that extremely rude.
• There are, however, some situations where it might be more acceptable to pick up the phone when you're with another person. An emergency is obviously one of those exceptions. A quick, important, non-emergency phone call is also acceptable. If you and your friend are going to meet up with somebody else, it's probably OK to call the person you're planning to meet up with, if say, you need to give them directions or tell them you're running late.
• The family dinner table is never an appropriate place to text. It may be different with your friends, tough.

And finally...

• It is never, ever, ever acceptable to text while driving. This one should be a no-brainer. Pull over. You may insist that you're good at it and that you can do it without crashing, but remember that there are other people on the road. Driving requires your full attention.