iOS 7 introduces a great new feature for users on limited data plans: You can now track how much cellular data is being used by each app on your iPhone or iPad and even disable access to cellular data for specific third-party apps. This is a big improvement over prior versions, where only an aggregate cellular data counter was provided and little to no control over which apps could cellular data.
You can access this feature form the Cellular section in the iOS Settings app; scrolling down will reveal a list of the third-party apps installed on your device. The amount of data used by each app is listed under the app’s name, and a switch to the right of the name allows you to disable cellular data for the app on an individual basis. A section at the bottom of the list provides information on any data used by apps that have been removed from your device as well as a detailed list of data usage by each built-in system service.
Note that this information only affects cellular data use; data used over Wi-Fi is not counted in any of these figures, and switching an app off from this screen will not prevent it from using data while on a Wi-FI connection. These counters will accumulate until manually reset; the “Reset Statistics” button at the very bottom of this screen can be used to reset all data counters—a good idea to do at the start of your monthly billing cycle if you’re trying to track data usage against your monthly allotment.