With you being in USA & I'm in the UK I'm not sure if this will help
I've done the firmware update to get on the DSWare (I'm now showing 1.3E) & I can tell you that my DSTTi still works (I use YSMenu but it still works with TTmenu)
I can only guess that if your firmware is 1.2E (or something like that - I'm afraid I didn't note what I had beforehand) then I guess it's the same firmware used whether you're in Europe or USA. Unless there's a design difference between a USA & a Europeon DSi I can't see any problem
If you're not sure on how to find your firmware version then follow these steps:-
Switch on DSi & select the System Settings option - in the top screen, bottom right corner, you should be showing the version number
UPDATE: Important Just found this thread @
http://gbatemp.net/index.php?showtopic=146229 that states that USA firmware is in fact '1.2
U' and that Acekards 2i are having trouble being recognised (they show up but don't run) - so I'm guessing that the USA DSi
WILL lock flashcards unlike the Europe ones. Whether it'll lock just the Acekard or all DSi compatible flash cards I can't say
I'm afraid you will either have to try it yourself or hope that someone else in the USA will reply saying that they have done it & it work - sorry couldn't be any help