Wifi isnt used by any games yet. Nintendo has talked about bringing games online but it hasnt gone down yet. I wouldnt hope for it for a YEAR. Let alone in games coming out in the next few months.
If you want to chat, go to aim.com and download aim. Sorry, the DS pictochat program is a neat little thing but its main function seems to be for when someone is in the relative same area as you (same house, a floor or two up in a building etc) but cannot talk to you in person for some reason. Seems kind of pointless in a way but I guess it could be used for classrooms (I wish DS was around when I was in high school
). Besides that you cant use pictochat and play games at the same time. So far multiplayer games dont seem to have chat built in, which makes sense considering somewhat limited screen space in a portable (yes even with two screens).