The game Pokemon does not exists for Android-based mobile phones but instead you may use a GBA emulator (Gameboy Color A.D.) which works with roms (please keep in mind that using ROMS which you do not posses might violate the laws of your country). In order to play Pokemon games, you need to have the original cartridge of the game before playing it. Once you dump the game to a GBA file you can load it on your phone in the emulator and play the game.
