Ps2 controller to iphone 4 converter?

i have a converter for my ps2 controller to plug into my wii controller so that i can play emulators on myiphone. is there a cable that converts my ps2 controller to iphone connection? i seen videos on you tube that people managed to plug snes controllers into the iphone to play emulators. i would to beable to plug my ps2 controller into it. either a converter or a wireing guide to make my own cable would be great. thanks.