iPhone hacking geniuses have already brought us the Nintendo Entertainment System (NES) emulator, the Game Boy Advance (GBA) emulator, ScummVM, the emulation engine that allows you to play popular LucasArts and Sierra games and Playstation (PS1 or PSX) emulator for the iPhone.
And if you are still not satisfied, then ZodTTD who had released the first public version of the Playstation (PS1 or PSX) emulator for the iPhone and iPod Touch has recently ported TurboGrafx-16 emulator, Temper, to iPhone.