If you're in a restaurant and you have to call someone or take a call, step outside.
If you're at religious services, a wedding, a funeral, etc. for heaven's sake
turn your cell phone off. It's disrespectful.
If you're driving, you should not be talking on your cell without a hands-free unit (unless you pull over or it's an emergency). In many states it's against the law, but more than that, it's unsafe to have one hand dialing your cell phone while the other one holds a venti mocha latte and you are driving at 80mph while steering with one knee.
