Apparently some clever guys at supermono have mastered it 
No one said it wasn’t possible on an iphone. It’s just that in a real game the framerate will not be playable.
the NGP by the end of the yer might be the first to dream of it, perhaps on a good day …
And the video there shows the performance problems … thats an itouch 4 and it stuttes and that with this little work and such simple shaders on the environment (I only see diffuse, neither normalmapping nor specularity, not considering the death strike of deferred + alpha overdraw)