From a cabin crew members perspective, it is very difficult to police this area of inflight safety, mainly because technology is changing so quickly and what one thinks isn't safe one week appears ok the next.
There was a pax on my flt a couple of weeks ago with a similar question and he just showed me the phone and user guide which indicated to me that this particular handset was ok to use inflight for music. So he "grooved" away for the duration of the flight (in a very Dad at a wedding kind of way!!)