Why does the screen come on when my phone is plugged in but idle?
The same happens occasionally on my Galaxy S, usually about 5-10 minutes after plugging in. If you can handle the dev tools, you could try charging the phone from an USB port while running logcat and checking what goes on around the time the phone activates, or if the screen turns on only when charging from a wall socket you could run aLogcat on the phone while charging and then try to see the reason, but it can be a bit tricky on the phone.