You can trade, battle, and have voice chats with your friends over Wifi in Pokemon Diamond/Pearl, but to do so you need to know your friends' Friend Codes, and your friends need to know your Friend Code.
Chat with our AI personalities
in jubilve city
because you need better wifi
In Jublife City
either by cheating or a wifi event (but wifi event expired)
WIFI connection and then put happy together. GOT IT PAL!