It works this way – you place the Hyperkin Smart Boy onto your smartphone, where data from the cartridge will be sent into the device’’s ROM. From there, it is anybody’s guess as to how the game will run, although it is most likely that an emulator of sorts will see action. Still, it remains to be seen whether Nintendo is going to approve of this, since they are notoriously known to be extremely protective of their IP, whether it hails from a couple of decades ago or otherwise.
However, that potential situation does not seem to faze the folks over at Hyperkin at all, since they do seem to be working on models that will target the iPhone 6 Plus as well as other Android-powered devices.