The FAA still doesn't have a definitive answer on the dangers of in-flight interference: Devices are designed to only work on specific frequencies, but there's concern about spill-over. This article doesn't mention it by name, but there's also an issue of harmonics in which certain kinds of reflection and opacity to radio signal can produce much fainter signals in entirely different bands.
The answer? Each carrier still makes up its own mind, and private charter flights typically allow any device.