I'm no genious, but i'm quite sure you have to be in range of an access point to be able to get onto Wireless internet. The only way to get on the net anywhere is through GPRS, the thing phones use, but theres no way of doing it on the DS as far as i know. And even if there was a 64k connection would be pants, and very expensive.
from anywhere? i doubt it.. the only possible known way i know is from access points. pretty much anywhere with an unsecured router. well secure routers work too but youll need the code/password.