I had the same problem with the usage and how it was the same as the standby time, but I fixed it. Follow these steps:
1. Plug your iPhone into your computer, and remove any stupid apps you dont want (dont delete them, just remove them from your phone).
2. Sync your phone, and than unplug it.
3. Turn OFF your phone (you've probably never done this, but you hold down the LOCK button on the very top of the iPhone).
4. Wait about 3 min (long time without a phone for alot of you eh?)
5. Turn it back ON.
It worked for me, and Im sure itll work for you.