I found these rules floating around on an internal mail distribution list- I thought they were pretty good, and wanted to post them here for future reference.   I’ve done some minor editing here and there, and cleaned up the formatting a bit… feel free to share this with anyone who may need a refresher ;)

1. Keep your phone in your pocket.  Taking out your phone and putting it on the desk during a meeting (or worse, on a table in a restaurant) tells the people who are physically present with you “Everyone else that I know is more important than you. If *anybody* wants to contact me, I am willing to interrupt our time and give that other person my attention”.  If you absolutely must have your phone out, then you essentially need to ask permission, or at a minimum, explain yourself. For example, “My wife is pregnant, and may call asking me to rush her to the hospital.  do you mind if I keep my phone out, just in case?”, or “My boss let me know that we’re having a major problem with a client, and that I must take their calls immediately if they need me…”, or “my wallet was recently stolen, and I'm waiting for my bank to call back and tell me that no one is using my charge cards”  are all acceptable.
2. Keep your phone on vibrate. no one wants to hear your ring tone.  *no one*. if your phone vibrates while it’s in your pocket, don’t take it out (unless you have a suitable reason that you’ve already given your physical companions… see above). the vibration shouldn’t be a demand for your immediate attention.  Just remember that there is something that may be of interest on your phone, and remember to check it when you have some free time.
3. polite app usage: before you check the score, search the map, tweet, update, search, scan, poke, shuffle, shake or do any other of the other wonderful things that your phone is capable of doing, tell your physical companions what your doing, and why you feel the need to do it *right now*.  examples: “what you just said was hysterical, i have to tweet that so that i remember it in the morning!” is ok, so are “wow, i wish i could remember the name of that restaurant, one sec, let me check the map”, and “ugh, i can’t remember the name of the villan duck on duck tales.  give me a sec, i know i can find it on wikipedia”.  just taking out your phone and tapping away at it while someone is talking to you is not ok. 
4. Excuse yourself when you are accepting calls.  No one wants to hear your half of whatever conversation you are having.  Further, everyone else should have to stop whatever natural conversation flow is taking place so that you can have your conversation. Further still, the person on the other end of the phone may not know (or appreciate) that you are not alone, and may not want to talk to you when others are present.  So, if you absolutely must take a call, excuse yourself, physically separate from your companions, quietly take the call, and then return.
5. Use your bluetooth headset properly.  Headsets are meant to be used in situations where actually holding your phone to your ear would be uncomfortable, inconvenient, or dangerous- for example, during a particularly long phone conversation, while using one or both of your hands (e.g., typing), or while driving.  If you actually can use your hand, you shouldn’t be using your headset.  Headset microphones and speakers are generally inferior to the ones built into most phones, and the interference from bluetooth will degrade the quality of your call.  you and your caller would probably both enjoy the call more if you don’t have to use your headset.  Never, ever, ever use your headset in public or in social settings. 

The basic premise behind all of these rules is simple: the people who you are physically with at any given moment should generally be given more attention that everyone, and everything else.  If there is something more important or more interesting than the people around you, then you should excuse yourself, and go tend to the more important, more interesting things that are fighting for your attention.  This is just generally good advise, regardless of whether a phone is involved or not.  The problem that many people have with mobile phones is that they act as though having an always-on connection to the rest of the world somehow excuses them from this basic premise of person to person interaction. It does not.