To reduce data usage, make sure you turn off cellular data and set your phone to “airplane mode.” You don't want your phone to grab data the minute you take it off airplane mode, even for a minute. Turn off or restrict background apps that refresh or update automatically, using data even when the app is closed.
Do: Turn Off Data Roaming. Before you get on that plane (or train) to leave the country, turn off both data roaming and cellular data on your phone. This will prevent your device from connecting to towers or networks along your journey, leading to pricey roaming charges from your carrier.
Do pilots know if your phone isn't on airplane mode? Well, sort of. “The flight attendants or the pilots are not going to get an indicator that says 13A has their cell phone on,” Laurie says. “But if there's enough people that they still have it on, and they're encountering that interference, then, yes.”
Can I text on an airplane? Yes, but only using a Wi-Fi connection. The ban on using a cellular connection means passengers can't send SMS texts. Any communication has to be over Wi-Fi with a messaging app that provides similar functionality like iMessage, WhatsApp, or Viber.
Why are airplane passengers asked to put their phones in airplane mode? Per the FAA website's Safety Information page, “The FCC and FAA ban cell phones for airborne use because its signals could interfere with critical aircraft instruments. Devices must be used in airplane mode or with the cellular connection disabled.
Does your flight attendant know if your phone is in flight mode or turned off? As a rule, no. There's no device that's regularly installed on airplanes that can figure out how many phones, tablets, e-readers or other kinds of device are on in the cabin.