I think your problem was more that it was an airtronics. I have used many, and every single one had intermittent glitches that the facotry couldn't figure out, and that was before cell phones were thought about.

Might have been anything. Who knows. Could have been the cell, could have been the guys keys in his pocket, could have been the plate in his head.

Tough call on that one. Wasn't there, would sure do more tesing before I flew it if it were my plane though.