Nintendo DSi Web Browsing Without an Access Point? Impossible (Requires Discontinued Hardware)

Impossible. The DSi has no built-in Wi-Fi radio—it requires the Nintendo Wi-Fi USB Connector (discontinued) plugged into an internet-connected PC to create a soft access point. Without that hardware and a host PC with internet, the DSi cannot reach the web.

Even with the connector, you're still dependent on a wireless access point (the PC's shared connection). There is no cellular, Ethernet, or direct-modem option for DSi.

Modern alternative: Use a smartphone hotspot + a hacked DSi with custom firmware (TWiLight Menu++) and homebrew browser—but that's far beyond stock hardware.