Huh, well thats disappointing
Apparently Pokemon Platinum doesnt use the DSi's advanced internet settings and in turn, does not support anything with WPA/WPA2 security, which is most things these days.
I know I might be able to set up a hotspot or get a cheap WEP router to use this on, but the GTS isnt that important yet. Hopefully HG/SS does not have the same restrictions so I can at least still use the GTS, as Pokemon Black 2 supports DSi connection settings just fine.
