While we are all eagerly waiting for Nintendo 3DS to arrive, here is one more bad news. Nintendo has place region lock restrictions on
its new device. Reportedly, a Nintendo Japan support officer has been quotes as saying, "There are no region codes in DS and DS Lite, but DSi, DSi [XL], and 3DS have region codes." We will respond with an "Ouch". The region codes are not only embedded in the device itself but will also be etched on to the individual games. So, effectively you cannot play a game on your device if the region codes do not match.
For DSi and DSi XL, region locking has ensured that you could access only your own region's DSi Shop. Also the DSi enhanced games are locked to the region of their release. It looks like the region code on 3DS will work in the same way. So no luck playing Korean 3DS game on your Japan locked 3DS. Since, the reports are unconfirmed, we will just wait for the official comments from Nintendo.
Source: JoyStiq