"I am not aware of whether making phone calls is a problem"

Most certainly is .... chatting about "onboard rules" in the pub one night with pal of mine who flies Dash 8's for a living,- he mentioned that that earlier that day they had just vacated the runway at Gatwick when he was unable to hear what the ground controller was telling him - due to that strange "dit dit dit" noise in his head phones caused by probably more than one of the passengers in the cabin switching their mobiles on.