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.