Originally Posted by docbert

United 777's do not have seat-back IFE systems in Economy, only in Business and First.

Their headphones in economy use a standard 3.5mm headphone socket (ie, the same thing as on an iPod or any other portable device).

In Business and First it's the same plug, with a second plug for the power for their standard noise canceling headphones. Any standard headphones will still fit, using the first plug only.