Friend codes are game and cartridge specific "addresses" assigned to every player that uses Nintendo Wi-Fi Connection. Each friend code is a combination of the game and the Nintendo DS that game is in. If you use your game OVER WI-FI in a different Nintendo DS, your friend code will change, and it will change to a new friend code every time you use a different Nintendo DS. The codes are usually assigned one per player, per game; the codes allow a player to store a list of friends with the same game and play with them when both parties are online. The codes come in different formats for different games. For example, the codes of Mario Kart DS and Tetris DS are six digits followed by another row of six digits, while Animal Crossing: Wild World's codes comprise three groups of four digits separated by hyphens. Friend codes in Mario Kart DS and Tony Hawk's American Sk8land allow the player to search for opponents that are in their friend list and are also searching for a match against "friends" with the same game. In Animal Crossing: Wild World, friend codes are absolutely required to visit another’s town via the Wi-Fi connection, perhaps due to Nintendo’s privacy concerns or the potential in-game vandalism that could occur from unauthorized visitors to the player's town. Adding a friend can also allow text and/or voice chat, as in the case of Metroid Prime: Hunters and Animal Crossing: Wild World. In "Animal Crossing Wild World", every Wi-Fi users codes of which you obtain, are stored in your "Friend Roster" so you can keep a record of whose town you visit.
On July 18, 2006, a page was leaked on Nintendo's official website stating that Wii would use the Nintendo Wi-Fi connection in much the same way as the Nintendo DS does, with a Friend Code system and no charge to play.[5]
