From Bulbapedia, the community-driven Pokémon encyclopedia.
The Pal Pad (Japanese: ともだちてちょう Friend Notebook) is a key item introduced in Generation IV and used again in Generation V. It allows players to register friends, who can be met in the Wi-Fi Club to battle and trade Pokémon.
The Pal Pad is obtained early in each game. In Pokémon Diamond, Pearl, and Platinum, Teala will give players the Pal Pad the first time they enter the basement of any Pokémon Center after arriving in Oreburgh City. In Pokémon HeartGold and SoulSilver, Teala will give the Pal Pad after the Zephyr Badge has been earned. In each of these games, obtaining the Pal Pad is not a compulsory part of the game and may be delayed indefinitely. In Pokémon Black and White, however, it is given to the player at Fennel's house by Amanita once the Striaton Gym is defeated and the Dream Mist retrieved from the Dreamyard. In Pokémon Black and White Versions 2, the player obtains his or her Pal Pad from the start of the game.
Adding a Friend Code in Platinum
The multiplayer components are run from the Nintendo Wi-Fi Connection. On this network, each game has a unique Friend Code, which can be exchanged with others to meet in the Wi-Fi Club. In order for a player to connect with a friend online, they must each register the other in their own Pal Pad. Registering a friend requires knowing their name and Friend Code; however, the name entered does not need to match the friend's actual player character's name. Friends can be registered manually by entering their Friend Codes into the Pal Pad, or automatically by trading Pokémon with other players in the Union Room.
Besides registering friends, the Pal Pad can be used to list registered friends and read the player's own Friend Code. The player's Friend Code is obtained when connecting to any place in the game having a Wi-Fi compatible activity, such as a Pokémon Center or the Battle Tower for the first time. The Pal Pad also records how many times the player has traded, or how many times the player has won or lost against another player in a Wi-Fi battle. In Pokémon Platinum and Pokémon HeartGold and SoulSilver, the Pal Pad also records how many times the players has won through the Battle Frontier's facilities with a friend, as well as the number of times the players have played Wi-Fi Plaza Games together. The Pal Pad can register up to 32 friends.