The 3DS' region locking is a source of considerable frustration for those who have enjoyed playing games from other territories on past generations of Nintendo handhelds.
On pre-3DS Nintendo handhelds, you could buy a game anywhere in the world confident in the knowledge that you'd be able to play it on your system. But for some reason, Nintendo chose to implement region locking on the 3DS, even as such a practice is becoming less and less popular in the industry as a whole.
For those of you willing to get your hands a little dirty, members of the "underground gaming community" GBAtemp.net have uncovered a means of circumventing the region lock and consequently being able to play games from any region.
Full instructions are here, but it's not a particularly easy process if you don't already know what you're doing with hacking the 3DS. Note that the trick will only work on 3DS systems running old firmware, too -- it's designed to work on systems that are running version 4.5 of the firmware, whereas we're now up to 6.3. This means that if you've already updated your system to the latest firmware -- which you probably will have done if you've been playing recent games like Pokémon X and Y -- you'll need to acquire a 3DS running the old firmware in order to take advantage of it. Still, a locally-acquired used 3DS that you don't mind tinkering with is probably cheaper to pick up than an imported system from another territory -- and if you manage to successfully apply the trick described, you'll have a system that will be able to run games from any territory.
Unlike many other region lock-breaking exploits, the trick does not open the door to piracy. Like any exploit, though, there's a significant risk of disaster if you don't know what you're doing, so follow the instructions at your own risk.