You can even use an iPad with 3G (or 4G for that matter) in the plane as long as you put it into "Airplane Mode" so all sending and receiving is deactivated.
Many airlines now offer Wi-Fi on board the plane during portions of the flight (the part that doesn't involve takeoff or landing). There will usually be a fee, though some airlines are experimenting with free service or at least certain services for free (like Facebook access only) in an effort to keep passengers docile.
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