it's a new combo port, combining the microphone and stereo headphones into 1 plug

i can see the elegance of doing away with the normal 2 plug system but am rough with my headphones and like being able to swap them around with mp3 player etc and replace when needed with stuff from the $1 shop

presumably headphones with the new plug won't be able to be swapped with older style units and won't be available for $1 for a few more years