I haven't got my Gateway 3DS in the mail just yet, but I've read that it supports ROMs from any region. It probably also supports retail carts from any region, provided that you're running them in Gateway Mode EmuNAND. Sky3DS, on the other hand, does not support any ROMs from other regions, unless you use smealum's regionthree hack. Regionthree works for retail carts too, but it isn't guaranteed to work for every foreign cart. The best bet, if you want to play games from different regions, is to get a Gateway 3DS flashcard. With it, you can either import foreign games or pirate them, provided that your 3DS has a SysNAND firmware version of 9.2 or less. Sky3DS and regionthree, on the other hand, can be used on firmwares 9.0 to 9.5 (but not all games run well with it).