Not that it should be of any surprise since Nintendo did make the announcement nearly a year ago, but we have confirmed with a US retail DSi-enhanced Nintendo DS game that Nintendo DSi-capable cartridges are indeed region locked.
Our test subject: James Patterson's Women's Murder Club: Games of Passion, one of the first DS cartridges featuring DSi-enhanced camera functionality released in the US. On a US system the game boots up fine, but on a Japanese system the game's icon will not appear in the system menu, preventing it from playing on that system.
The lock-out does not apply to playing the game on standard DS or DS Lite systems, as those handhelds don't have the same specific territory firmware as DSi units.
Some users speculated that the DSi lock-out would be limited to the DSi Shop and DSiWare downloads, as the territory determines which online store the system will connect to. But this confirms that the lock-out also includes cartridges.
This is a big deal considering that the DSi is the first handheld system from Nintendo that features region locks. Nintendo mentioned last year that the reason for the cartridge lock-out is due to the specific internet connectivity of the system as well as the incorporated parental controls that use each territory's unique rating standards.