........and also that other passengers may not appreciate the phone use, and so go outside to make the call.
Preferably at 35,000 ft !!
There's more chance of people annoying other passengers by using a mobile phone than there is of them blowing up the aircraft as a terrorist, so let's turn all the airport security devices into mobile phone detectors - and confiscate them.
Not so many years ago passengers were totally incommunicado for up to 12 or more hours once they boarded an aircraft. The World didn't end, nothing is that important.