Turn Cellular Data on or off
Go to Settings > Cellular Data. If Cellular Data is turned off, all data services 
will use only Wi-Fi, including email, web browsing, push notifications, and 
other services. If Cellular Data is turned on, carrier charges may be incurred. 
For example, using certain features and services such as Messages transfer 
data could result in charges to your data plan.
Turn Data Roaming on or off
Go to Settings > Cellular Data. Turning off Data Roaming avoids carrier 
charges that may arise when using a network provided by a different carrier.
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Chapter 25
Settings