bob is right, a lot of people leaved them plugged in overnight which wastes energy. What most people don’t know is that even when the phone isn’t plugged in, but the charger is, it is still wasting a lot of energy! Sometimes, the adapters plugged into the wall even get warm, which is a total waste of energy. I can’t remember exactly how much, but many things that remain plugged in all the time, like your tv, waste incredible amounts of energy. I remember from somewhere that a tv, while off, was still using 90% of the power it uses while on. If you leave things plugged in, which everyone does, you can use a surge protector or something, and just flip the switch on it to cut all power.
Of course, it is a cell phone, so your not saving much, but you are saving more than just what it takes to charge it. I built a solar phone charger last summer for fun/learning experience. It has a cigarette lighter connection so I can use for a lot of stuff :)