Once a DS has been flashed (skips the health and safety screen) it also disables signature verification for DS download play, so you can beam homebrews directly to your DS' home screen with a wifi card. But this is an awkward process that most people don't actually do with their original DSes, as it requires putting tinfoil over a toothpick and jamming it into a hole next to the battery to close the flash write jumper. I think DS' crypto has also been defeated but I can't find any documentation of arbitrary download play on unflashed DSes. Also seems no .nds signing keys in the leaks from what I can tell.