I sent you this as PM but I figured it's very useful information, so I'm gonna paste my response to this reply

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INTERNET AND POKEMON
With Generation IV (Diamond/Pearl/Platinum/HeartGold/SoulSilver) and Generation V (Black/White/Black2/White2), you get to use your NintendoDS/Nintendo3DS's online connection (using your wireless router at home or at a hotspot) to connect your handheld to the Internet.
CONNECTING ONLINE IN-GAME DURING THE STORY
Upon starting the games, usually around the 2nd or 3rd badges, the 2nd floors of Pokemon Centers around the towns in those worlds will open up, allowing you to use something called the "Global Terminal" to connect to the Internet using WiFi and battle, trade, etc.
HOW IT WORKS
The way it works is, it takes your cartridge's unique savefile number (generated secretly when you create your save) and your handheld's connection to create an unique ID number when it connects online. There are no serial numbers (not 'really', though you do have a 'pal pad code' which works like a friendcode if you want to trade with friends you know). It's a little complicated but you don't really need to know the details.
SOME THINGS TO KNOW
You should know, however, that what is done is, the Game's Save is combined with your handheld's Wireless Connection Information to generate an unique number that's saved in your savefile.
This little tidbit of info is not too important, but it's good to know. Also, this ensures that you can only do this with your game inserted in your own system. Note that if you own multiple handhelds (such as a DS, DSI, and 3DS) and try to change systems and then connect, the game will know, and will wipe out your previous connection's information and update it with the newer handheld. However, any promotion that you got will be saved, so you don't lose anything except your "Pal Pad Friend Codes" when you do this (it's basically like your cellphone number: it changes and you'd have to tell all your friends you've connected with that you got a new one, so you would have to write down all your Pal Pad friendcodes if you change devices).
POKEMON PROMOTIONS FROM NINTENDO, GAMESTOP, TOYS R US, MOVIE OUTINGS, ETC
Once your DS/Cartridge are configured to go online (i'm assuming your DS has been configured to go online already, otherwise that's a whole 'nother discussion), you can get Pokemon Promotions through the game's "Mystery Gift" option. When you fire up your game, before hitting "Continue" on your save, you have some extra options, one of which is "Mystery Gift". This feature was using in the old GBA titles, but you would have to either use a Wireless Adapter near a Game Store that was running the promotion, OR connect via a cable. THIS IS NO LONGER THE CASE. Now, you just turn on the game, select "Mystery Gift" and choose "Use Nintendo WiFi Connection (Nintendo WFC)" and it'll go online, and if Nintendo is running a promotion, it will download the "Gift" and save it to your game.
There are other methods of getting promotions. Sometimes Toys R Us or Gamestop, or if a new Pokemon movie comes out, these places will have a "Wireless" location. You would just have to use the "Mystery Gift" option while in that Wireless Location (usually inside the store/movietheater) and choose "Wireless" (instead of "Nintendo WFC"). If you do it this way and a promotional download is nearby, you will get it.
HOW TO CONNECT YOUR DS/DSi/3DS ONLINE (If you do not have a Wireless Router)
If you do not have home WiFi, you can go to any open WiFi hotspot (Try a McDonald's or a Starbucks!), and configure your DS to go online via those HotSpots. There are other ways to go online if you do not have WiFi, such as using a laptop (laptops usually have a wired adapter and a wireless adapter) in conjunction with "Internet Connection Sharing" to connect devices, but it varies between platforms/OS's/HomeSetUps, so it requires different methods to go online.
You can also purchase a "Nintendo WiFi Connection Adapter", it is an USB dongle that you connect to any computer that's wired to an Internet Connection, and it'll create an USB Internet Connection Bridge that'll let you hook up any Nintendo System to the 'net without having a Router. This is by far the easiest (and most affordable) way to connect a Nintendo system (works with NintendoDS, Nintendo3DS, Wii, and Wii-U) to the Internet if you do not own a Wireless Router and have a computer.
They're about $17 in Amazon (+Shipping & Tax)Promotions for Pokemon online usually run a specific number of days (it's usually a few months). For information on particular offers, you can go to the official Pokemon Global Link webpage (which you should go to anyway as you can, in the latest games, 'upload' a Pokemon to the Internet and interact with it online via flash software, a method you can use to get a number of Pokemon from the Internet).
Official Pokemon Global Link WebpageAnother good site for Promotions is the homepage of Serebii.net. Usually they tell you if there's a "Nintendo Event" download. Could be a new Pokemon. Could be a wallpaper for your in-game "C-Gear", would be a new play for one of the town's "contest plays", or what have you.
There's lots to do with Pokemon, your handheld device, and the Internet these days. I've only scratched the surface.