I've noticed that my usage time on my iPhone 4 increases slightly even when my iPhone is locked. For example, over eight hours, my usage increased 7 minutes. Over 40 minutes it increased 1 minute. My battery dropped dramatically after one night where it said my usage was 12 hours (all the time I slept). After that I restored, but I still see my battery usage increase slightly, even in lock mode. Does anyone know why this is, and if it's a problem.