Mario Kart DS has this nifty feature where you can “locate” your friends online for internet-based multiplayer. It’s pretty neat, but Nintendo pretty much requires you to distrubute your friend codes by word-of-mouth; there’s no central repository for friend codes on their site, and they’ve even specifically banned the discussion of trading these codes on their forums. So it’s the old-fashioned way for now, until some enterprising individual decides to make up a site for sharing codes.
Comments are enabled; leave yours as well. Any maybe if I get bored I’ll make up a searchable database or something.