If you're a fan of the DS, you'll be interested to see the photos of DS's headset, which has yet to be released. A matching set looks better than just any headset for sure, but these things will have to be quality if Nintendo wants people to buy them separately. Considering it is not a stereo set, it'll definitely have its work cut out for it, though it does include a built in microphone for online play. It's going to be very cheap, however, which may convince many to try it:

The headset will be released in Japan on September 14 for 1,200 (about $10 USD). Nintendo has not yet announced a release date for North American or European gamers.
Japan is probably a test market for other areas, so if it takes off there we can probably expect it in western countries as well.