A gaming enthusiast who wanted to play Nintendo emulators on his smartphone but didn't want to use touchscreen controls has created his own special controller by combining a Game Boy, Wii remote and a Galaxy Nexus.
Chad Boughton posted a video to YouTube showing how he got his phone to sit in a Game Boy dock while also getting the Wii remote to connect with the phone via Bluetooth.
Boughton explains that other hardware on the market didn't give him the gaming experience he wanted and he didn't want to have to plug anything into his phone via USB. So he decided to make something himself.
He writes on Instructables (with step-by-step images):
Using a Wii remote as the Bluetooth interface, and a Dot Matrix Gameboy's butttons and shell (two things I already owned) I figured "why not mash them together and give them a whole new purpose?". With the use of the "Wii Controller IME" App on the Play App store, this retro controller will really control anything which lets you use the android touch keyboard as input. Although i've only tried with a SNES emulator, in theory you should be able to play and do all kinds of things with the Gameboy's buttons. The project is essentially a gutted Game Boy with a Wii remote inside. The tricky part was rerouting the button connections between the two.
This project was built for the Galaxy Nexus, but can easily be altered to any Android phone or tablet. The limitation is really the support of your device with the Wiimote App. Technically you could control your wii with the Gameboy minus some functionallity.
More information on how to create the Game Boy gamepad can be found here.