I've just about had enough of this, I've tried everything! Restored my iPhone 4 on 4.2.1 to default settings and just synced my apps onto it - and still, I lose 25-30% battery every night (~10 hours) while the phone is in standby. It is NOT jailbroken. There is no app running in the background. Data and 3G are OFF. Have tried to drain it completely and then recharge to make the battery accurate - doesn't help. I guess I'll need to call it in?