If it were passenger/communication safety they would ask me to remove my headphones. They never ask me to do so.
I think it has more to do with multiple phones being connected to cell phone tower, rather than a single electronic device. And in that regard, had more to do with the old analog wireless wavelengths versus the newer digital spectrum. Those analogs sure as hell could throw out some radio interference. The FAA may have based their current policy on the analogs. Just a thought.
Not to mention edge can cause a nice buzzing sound in the pilots headphones.