DO you know we can use the headphone button to control the 3DS sound, if we go outside and take a 3DS, sometimes we will listen to the MP3 with 3DS , now a headphone which can control the music sound will be pretty good, and now it becomes true.
We can use some headphones such as the latest Apple ear buds to work on the 3DS and then control the sound, it is very easy , just switch tracks and pause (and then un-pause) your music.
Not a big thing but useful....
Video about it headphone for 3DS:
YouTube - 3DS