>>15242906I think as long as the connection is the right kind, the 3DS probably has the same type of jack that Wii U does (a combo jack). I just tested a dedicated microphone (i.e. just a mic, no earphones) and it silenced the music, which I certainly hope the one in OP doesn't (I'm not quite sure how it would avoid doing that, but maybe OP just decided "fuck the music").
Headsets that have one 3.5mm jack (rather than splitting voice and hearing) should support it for both hearing and mic. It'll look like a typical headphone jack, but with 3 of the black stripes instead of just two (pic).