Nintendo Wi-Fi Connection

Nintendo Wi-Fi Connection (WFC) is the free online service run by Nintendo. Several Nintendo DS and Wii games utilize the service for purposes of online multiplayer. The user merely requires a wireless internet connection to connect with either system.

Friend Codes
The service uses what are called "Friend Codes". These are 12- to 16-digit numbers that are swapped between players in order to add each other to their friend lists within the games. In most games on the service, the only way to reliably play with a certain person is to do this. Many games also come with an "Anyone" mode which allows the player to play with anyone who is connected, usually without functions that are present in Friend Code play (such as voice chat).

Zelda Games Utilizing the Service
To date, Phantom Hourglass is the only game in The Legend of Zelda series to use Nintendo Wi-Fi Connection. The purpose of the WFC in Phantom Hourglass is that of two-player battling in the game's multiplayer mode.

Criticisms
Nintendo Wi-Fi Connection is often criticized because it lacks many features which have become common and even expected in an online service. Features such as voice chatting are present in very few games, and the necessity of Friend Codes (as opposed to merely asking someone on a game you've played to be added to your list) is regarded by many as a poor decision on Nintendo's part.