The Usage feature is one of the places to go on your iPhone for statistics on how you actually employ the device. Your iPhone's Usage feature allows you to track several parameters.
The amount of time since you last fully charged your iPhone: This is indicated in days and hours, both for the time when the iPhone has been unlocked and used and when it's been locked and in standby mode.
Call time: Shown for the current period and the lifetime of the product.
Cellular Network Data: The amount of network data you've sent and received over EDGE or 3G. You can reset these statistics by tapping the Reset Statistics button at the bottom of the screen.