Which Pokémon games were the first main-series titles to use Nintendo Wi-Fi trading?

Pokémon Diamond and Pearl were the first main-series titles to use Nintendo Wi-Fi trading.

Released for Nintendo DS in Japan in 2006, Pokémon Diamond and Pearl introduced online communication through Nintendo Wi-Fi Connection. Players could trade and battle with others over the internet rather than relying only on a local link or cable connection.

The games added the Sinnoh region and a large set of new Pokémon. Their underground area, expanded breeding features, and online facilities helped make the Nintendo DS era a major technological step for the series.

Earlier games supported local communication in different ways, including the Game Boy Link Cable and later wireless functions. Nintendo Wi-Fi Connection should therefore be understood as internet-based service infrastructure, not simply any wireless connection. The service was discontinued in 2014, but Diamond and Pearl established the model for later online Pokémon games.