Turning off cellular data can help preserve your iPhone's battery life, as well as protect you from data overage charges.
How To Turn Off Cellular Data on iPhone:
Tap on the Settings app
Toggle Cellular Data to the Off position
So as you can see, turning cellular data off on iPhone is extremely simple. You can always return to the Settings app whenever you want to turn data back on.
It's worth noting that you can also turn on and off your LTE capabilities in this same Settings area, which can help you save battery greatly in times when you don't need the extra speed that LTE provides.
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