so this is kinda old news but since september, there has been a way to get on wifi again on Pokemon Diamond, Pearl, Platnium, HeartGold, SoulSilver White, Black, White2, and Black2
for anyone who may not now how to set it up, ill explain breifly here:
Go to your 3DS/DS system settings go to your current wifi connection. change DNS settings to 'dont auto obtain' and make the DNS the one in the link ill try to put up below
and save it as that. depending on your if wifi router is compatible, you should have no trouble connecting. note: it may change the DNS to: 188.8.131.52 (no 0 before the 44) wich is fine! it may do that, but it will still work.
there is another DNS you can try if that one does not work. they is a website with more info on how all this works/how to set it up. ill try to get link to it in a moment
Stella Glow, AC:NL, Denpa Men 3: Rise of Digitoll and Pokemon Pricross