id Software's John Carmack, the man who designed the engines for Doom, Wolfenstein 3D, and Quake, has personally overseen the development of Wolfenstein 3D for iPhone, the first project that id has done for the Apple platform. Originally, the intent was for id to do a version of Orcs & Elves, but that didn't pan out. And he was presented with a version of a Wolfenstein RPG that had great texturing, but a really bad frame rate. So, he optimized it and we are now graced with Wolfenstein 3D for the iPhone.
Carmack says that the episodic nature of Wolfenstein makes it easy to bring to the format, as it will be easy to sell in pieces through the App Store. The plan is to port other id titles to the platform if Wolfenstein is successful enough, which will likely include Doom and Quake. The open source port is available now, but the download through the App Store will be coming very soon.