You just put your 3DS in the charging cradle when you get home (it must be connected to your home network).
I don't know if SpotPass downloads these costumes automatically, or if it downloads a notice that something new is ready to be downloaded.
However, these new costumes DO NOT exist on the retail game card. So it's not just a code that you download to unlock content that is hidden on the game card, the content is entirely new and will be put on the SD card (because the game card is already maxed out in terms of space).
Also, there are not just outfits, but also different challenges that can be downloaded via SpotPass.
Spotpass should also work with free Wi-Fi networks that don't require an access code (like at McDonalds or something). Although you do need an access code if you want it to connect to your home network (or a friends' network).
Read the mania: http://www.fanfiction.net/~nonexistinghero In SA2, it's Super Sonic and Hyper Shadow.
In a Japanese interview at 4gamer.net, the producer explains that when you receive the spotpass DLC costume, you have to boot up the game and save it (on the same day), otherwise you'll lose it, even though you receive a notification. It's because the file size is too big or something similar...
Check out my Gaming Diary @ http://helugame.wordpress.com/ Now playing: Dissidia 012 Final Fantasy
shadowtemari posted... I assume a ds usb connector would all so work for a 3ds.
Only if you're reffering to the USB wifi adapter for nintendo systems, then yes that should work (as far as I can tell mine connected no problem, but I never use it anymore as my wifi network is significantly faster now than what the wifi adapter maxes out at). If you're referring to a USB charger, any ds charging cable (be it an Ac, dc, USB, etc) would not work with the 3ds as the charging port on the 3ds is drastically different from the ds's.
The led that is in the top right corner of the system (the one that lights up green if you street passed with someone) will light up blue when there is a spotpass notification (i.e. when a costume is available for download in DOA).