If you're plugged into DTV, there's no reason you shouldn't be able to have headphones in. I believe the DTV can be killed by the FA should something go wrong. I personally don't agree with not being able to listen to an ipod, etc, because it would take all of three seconds to rip it off and follow any crewmember instructions, but I've come to accept the policy and comply. After all, it would take me longer to orient myself after waking up then to take off headphones.