Don't forget: Today (Sunday) is the last day for downloading Raikou, and tomorrow (Monday) is the first day for getting Entei.
Dates:
Raikou - Mon 7th Feb to Sun 13th Feb
Entei - Mon 14th Feb to Sun 20th Feb
Suicune - Mon 21st Feb to Sun 27th Feb
If you don't have compatible Wi-Fi settings at home or one of those Nintendo USB thingies, you can find a DS-friendly Wi-Fi hotspot
here. They seem to cover pretty much anywhere in the world. If you have a DS or DS Lite, make sure you find a hotspot that specifically says "Nintendo Wi-Fi Zone" if you can, because a lot of other places seem to require you to accept their terms and conditions by ticking a ticky box on their webpage before you can use the Internet, which you can't do on your DS due to the lack of a browser. If you have a DSi, though, you're fine - you can use the browser to accept the T&Cs, and then load your Pokemon game up and get the Wonder Card in the usual way.
Alternatively, I have discovered that my phone has an app that allows me to set up a Wi-Fi hotspot using its mobile Internet connection, and some of you may have a similar thing. (Just please make sure you know how much - if anything - you'll have to pay for using the mobile Internet.) It should only use a couple of hundred KB of data to download the Wonder Card.
This event is officially for all European 4th Gen games (Diamond, Pearl, Platinum, Heart Gold, Soul Silver), and has also been confirmed to work for American, Canadian, Mexican (English-language), and Australian games.
If your game doesn't fall into any of the above categories but you find that you can get the event, please let me know and I'll add it to the list :)
Edit: Note that if you have already been to a Gamestop and got any of the shiny beasts, you will not be able to download that one over Wi-Fi. So if, for example, you've got a Gamestop Entei, you won't be able to get the Wi-Fi Entei, but you will be able to get the Raikou and Suicune.