The Global Terminal, known as the Global Trade Station in Pokémon Diamond and Pearl, is located in Jubilife City and Goldenrod City and is the worldwide network over which players of Pokémon Diamond, Pearl, Platinum, HeartGold and SoulSilver can interact in different ways via the Nintendo Wi-Fi Connection. In Sinnoh-based games, in order to access the terminal, players must have the the first badge of the region, while it is instantly accessible in Johto as soon as the player arrives in Goldenrod City (this may be due, of course, to the fact that one cannot get to Goldenrod without the first badge). The player's first Pokémon is returned to its Poké Ball before entering in HeartGold and SoulSilver.
http://bulbapedia.bulbagarden.net/wiki/GTS#Global_Trade_Station
