There are elements of the DSi that are region-free -- you'll be able to surf the 'net wherever you are in the world, exchange photos with friends in other regions, and still play non-local DS games on the DSi -- but it looks like we can forget about importing Japanese DSi software. It simply won't work.
Nintendo's messenger says this is because the DSi "embeds net communication functionality within itself" and provides "net services specifically tailored for each region." The fact that each region has unique age limits is also mentioned. What a thoroughly depressing start to the week! We're off for coffee and extra donuts.