Uploaded today to the Minna no Nintendo Channel is a free client for viewing Flipnote Studio animations (previously exclusive to the DSiWare application) on any model Nintendo DS. The client can be downloaded using the DS's Download Play function, and uses wifi to download and playback animations with sound. Users cannot create or submit their own animations using this client, it allows viewing only.
The application is entirely in Japanese, so the exact details of what it is or encompasses is a mystery to me; perhaps a friendly GBAtemper will make us a translation (hint). For now, the viewer is fairly usable without Japanese knowledge; upon loading, there's a few screens of text, after which you reach the title screen (seen above). The top option connects to the network using wifi, the bottom option allows setting up your wifi connection as per other wifi-enabled games. After connecting, three options appear on screen; the first shows thumbnails of all available animations, while the second and third access help pages of some variety, also over the network.