The Conventional Wisdom on FT seems to be that the threat of interference is BS because "I kept my phone on during the flight and we didn't crash". Not exactly a scientifically rigorous line of argument.

I did read an article in an electrical engineering journal several years ago that examined the issue. If I remember correctly, the issue was a real one, particularly for equipment that had been repaired (factory-installed shielding was often compromised/damaged during repairs). TV's and FM radios were the biggest concern due to the internal frequencies they used.