From the Home screen, navigate: Settings > Cellular.
View the overall cellular data usage.
Current Period Roaming
View the individual apps cellular data usage.
The app cellular data usage is displayed beneath the name of the app.
To turn cellular data usage for an individual app on or off .
Exchange ActiveSync accounts are handled separately from other Mail and Calendar accounts. Exchange ActiveSync accounts continue to use cellular data even if cellular data usage for Mail and Calendar are disabled.
To view the data used by system services, tap System Services.
The data usage is displayed to the right of the system service (e.g., Mapping Services 2.0 MB).
Tap Cellular (upper-left).
To reset the usage statistics, tap Reset Statistics.