The plug doesn't work. The two primary plugs are usually for left/right sound. The third one is usually to provide power for the active noise cancelling ability (notice there is no battery compartment usually). There may be a way to do some sort of workaround, but I would not know of one. You only need the two primary though (if you own ANC headphones, they often come with a ). The third plug is not required as the headphones should be powered by a batter. If you're looking at space consumption, I would recommend getting one of the ANC buds or IEMs... most are pretty small (think business card holder sized). Not the best noise cancelling, but comparable to airline cans (eg, ).

Second, I would not be plugging my phone or tablet into the IFE. While extremely unlikely, you can be juicejacked by opening up your file system like that (by agreeing to access the system) is asking for trouble. If you have personal/confidential information on the phone, be aware of the risks you are taking. You could have your phone probed and copied without you knowing if you accept that prompt.

Personally, I have a working QC25. while it may be bigger and clunkier (but I like the noise cancelling), since it stays in my luggage when I am not using it, it doesn't really bother me. I carry non-ANC earphones for when I am out and about. Makes things easier. All I need is a small stand to put my tablet/phone on to watch on the seat table...and a power bank to ensure that the phone stays charged (if the in-seat power is not working).