I'm new to the iPhone. As I had understood it, when the phone is fully charged and still on the charger, the plug symbol which appears on the batter meter indicates that the phone is being powered through the mains. Which is what I want, because when I work from home and I'm using the phone all day I don't want to be using the battery. However, I've noticed that if I start using the phone when the plug symbol is on, the plug symbol will eventually revert to the charging symbol again, suggesting that it hasn't been using the mains but has drained the battery a little. When I took it the Apple store, to be honest they didn't really have a clue what I was talking about and they gave me a new phone. The new one does the same thing. Can someone please clarify that when the phone is plugged in and fully charged, it should operate off the mains and NOT drain the battery? If so, do I have a faulty phone?