No one is ever locked up for making calls/using an app. You get questioned for not following direct orders from flight attendants. Up there, they are the law. If they decide you are endangering the flight they can inform the captain who decides to make a diversion to offload you sooner. Then you get not only questioned by police but also a hefty bill from the airline for the disruption caused.
The law is the law, not arbitrary statements of poorly trained people.