[nitrogen]

I've experienced noise from old phones on cheap computer speakers, alarm clock radios, and installed sound systems in churches. It's annoying, but if the interference is in the audible frequency range, I doubt it's harmful.

[xtdx]

How do you know there isn't interference in the inaudible frequency range? Because you can't hear it?

[nitrogen]

It's an inference from the fact that the phones pass FCC regulations. Maybe that's an invalid inference.