This is a quick tutorial to show you how to fit the USB PCB board from the GAMEBOY color cartridge to one of the vintage and original DMG carts.
You could do this mod buying the POKEMON special editions carts, or a white cart like this, just try to find the original TAMAGOTCHI JAPAN game, as I know...
http://www.gameboycarts.com/2009/12/how-to-set-your-bleep-bloop-usb-cartridge-into-one-old-school-game-boy-cart/