It seem that even though Nintendo has managed to block the majority of the flashcarts or homebrew devices in their new version of the amazingly popular Nintendo DS device, called the Nintendo DSi - there are already some flash card devices out there that will work on this new model.
I think Nintendo may be going the "way of the wii" or PSP where firmware updates may be forced on people to allow them to play the latest games - but will also update the firmware to the latest version with more patching against the software pirates and DS homebrew community. Cards like the M4 which are so popular that Nintendo had to get legal rulings to shut down their production in Japan and China are used, in conjunction with a MicroSD card to download ROM images of the games off of the internet and then played on the Nintendo DS.
At the moment, the only card that can do this on the new DSi model is the Acekard 2i.
You download the ROM images, drop them onto the memory card, put it in the DSi and play the games! Wifi gaming is supported, as is game saving and built in cheat file support. It remains to be seen how the new set of games for the DSi will work with this new device. There have been no games so far that allow for usage of the new front facing or rear facing camera on the DSi.
I am pretty sure the only place you will be able to get one of these Acekard 2i things is on eBay. Let me know how you get on!