It's called 3G4 (get it? because G kinda looks like a 6?) and the iPhone Nintendo N64 emulatior is actively being developed by a 14 year old developer. You'll notice in the demo below that it is running pretty well at scaled down resolutions.
Things on Doogy's to-do list: overcome duplicate button registers, delayed presses, and some crashing -- and he has yet to implement the L, R, and Z keys. It is due out next year, probably on a Jailbroken platform like Cydia or Rock.
