Access Usage Manager to view data usage, set data limits, and see the apps using the most data.
INSTRUCTIONS & INFO
To view data usage via the Usage Manager, from the home screen, tap the Apps icon. Note:To check your current month's data usage dial *data# (*3282#) on your mobile phone to receive a text message with the current bill cycle's usage.
Scroll to and tap Usage Manager.
Scroll to view the data usage summary for the selected billing cycle.
To change the displayed billing cycle, tap the Data usage cycle drop-down.
To change the billing cycle start date, tap Change cycle.
Select the Desired date and tap SET.
To set a monthly data limit, from the quick settings menu tap the Settings icon.
Swipe to the CONNECTIONS tab, then tap Data usage.
Tap Set mobile data limit checkbox. Note: When the mobile data limit is active and has been reached, the mobile data block will remain in effect until mobile data is manually re-enabled on the device, the limit threshold is changed to a higher value, or a new data usage cycle begins. If you set data usage limits on your device, they do not communicate with AT&T systems. You will still receive AT&T system generated notifications as you approach your data limits.
Drag the Warning marker up or down to set the level at which you will be warned about your monthly data usage.
Drag the Limit marker up or down to set the monthly data limit.
The data warning and limit will save automatically.
Scroll to view data usage broken down By application. Note: To restrict apps from using data while running in the background, from the Settings menu scroll to the General tab > tap Power saving > Power saving mode > Toggle Power saving mode ON > Restrict all background data.  Your myAT&T account is also another way to manage your wireless usage.