read what user above said (nintendo shutted down servers, you must use fan made servers)
and keep in mind, as dsi (and DSI GAMES) supports WPA security, DS games don't support it.
if you want to play online with DS games either change your router security to wep. or none security
protip: WEP security only protects you against your grandma using your internet, anyone with a computer (or phone) can easily read a WEP key.
so only change your router temporary (like 30 minutes) and if you know what you are doing.
cuz your neighboor can use it for evil stuff and it will be your name on the bill\letters