How to check & lower your iPhone mobile data usage
Checking your usage:
To check how much mobile data your iPhone has used on each application go to:
Settings -> Mobile -> Mobile Data Usage -> Use Mobile Data For
Here you can see how much of your iPhone’s data each application has used, and turn off any applications you don’t want to use your data on.
To switch off an application, simply swipe the green switch to off. This will prevent the app from connecting to the internet via your mobile data. Instead, the app will work only when you access the internet via a Wi-Fi network connection – a far cheaper alternative!
You can reset these stats whenever you want.