Although I'd like to lay down the law for all circumstances, this is mostly aimed at the office. This is similar to the Men's Restroom Etiquette that I've worked on before — not wholly definitive, but certainly official–ish. Here you go (in no particular order):

The convenience is more for you than it is for them

Although your spouse/significant other now has you on a shorter leash than ever, it doesn't mean that you have to answer every call. If you're in the middle of a meeting and you receive a call, you don't have to answer it. If it's important, they'll probably leave a message. If it's really important, they'll probably call back.

Don't call, send a text message

Not everything is worthy of a phone call. Sometimes you just need to get a message to somebody, but don't need a full-blooded conversation about it. Send a text message, and when it's convenient, they'll get back to you. If you want to know about some financial matter at 9 o'clock at night, send a text message. The banks are closed, it's not a super-pressing issue, but you'd still like to know.

Vibrate

Your phone doesn't have to make noise in order for you to know you're getting a call. You probably carry your phone in one of two places – your pocket, or your purse. If it's in your pocket, it doesn't have to ring at full volume so that you can hear it. The magic is in the vibration. If you need a little extra help, have it do a little ring as well to get your attention. Purse? A quiet ring will do – no need to set it at full volume.

Not everybody loves your ringtone

Movie themes, catchy jingles, the default ringtone – we've heard them all, and we're not even in the same room as you. The key to a ring tone is to be subtle. A little ticking noise, or a gentle ring - that's okay. Donkey Kong Country Music? Nokay.

You're not cool just because you have a cell phone.

In case you hadn't noticed, you're now part of a majority of people, not a minority. You don't have to carry your cell phone in your hand all the time, and try to get people to notice it. There is no need to wear it on your belt and constantly take it off to look at the time. Yes, we've all seen one before, and probably that model as well, so we don't need to hold it, look at it, or talk about it.

We don't want to hear your conversation

It's a phone, not a can on a string. You don't have to yell. If you need to talk for an extended period of time, remove yourself to a different location. As much as you may think we care about the proper steps to feed your stupid cat… we don't care at all.

Hands-free sets are for cars

To begin with, lots of the newer hands-free sets look like something from a bad (was there ever a good) episode of Star Trek. So, as you walk around acting like you're all important with your cell phone, and the call you're on… you look retarded and crazy. Do you actually need both hands to do whatever you're doing? Probably not. Stop making it look like you're talking to yourself.

Cashiers have feelings too

Great, you're on the phone at the store. You're trying to multi-task. The downer is that you're being pretty rude by trying to carry on two conversations at the same time. You're also being rude if you're completely ignoring the cashier. Just tell the person to hang on for a moment while you finish up at the store. Converse briefly with the cashier, thank them for their help, and be on your way. The person on the phone can wait the 10 seconds that whole process took, and you finally responded well to the cashier who's been asking you questions all along.

I think you get the point here. Although I could go on with more things that have less and less to do with the working environment, I won't. Driving, movie theaters, other public places, restaurants – all very crucial times during which your cell phone usage is being scrutinized by others around you.

I kid you not – today at lunch, there were four people sitting at a table, obviously there together, and all four of them were on their cell phones. I'm sure they had a great lunch with each other. (I'm don't need to delve into the one among them who was smoking in the very clearly marked non-smoking area)

Carry on with wisdom in these choices. Please feel free to add your own words of wisdom below. Thanks to Clifton and Jenn for help on this one.