Doom Resurrection and Wolfenstein 3D Classic are only the beginning for id Software on the iPhone, with everything from Wolfenstein RPG to the upcoming Rage making their way to Apple's platform.
As a matter of fact, Wolfenstein RPG has been completed for quite some time. As id's John Carmark explains it, his excitement over getting Wolfenstein 3D Classic on the iPhone screwed up EA's release plans a little bit.
"I was disappointed that EA decided to sit on it, but they kinda freaked out when I did the Wolfenstein 3D Classic, as it wasn't a carefully planned thing...I just thought "Hey, This is cool and fun, let's release it!" That blew their planned rollout - they were worried about selling people two Wolfenstein titles at once. Hopefully they'll release it soon."
In the meantime, id Mobile is working on finishing the Doom II RPG for cell phones, after which they'll be doing that for the iPhone. Carmack himself is running the classics line, which will see the release of Doom, Quake, Quake II, Quake III, and then there will be more from scratch titles. One game he mentioned specifically was Rage, which would be "a destruction action thing".
Finally, Carmack is interested in creating a technical proof of concept for running the idTech 5 megatexture content creation pipeline on the 3GS, simply to warm the technology up and see what the more powerful device can handle.
All of that, plus working on id's big titles? It doesn't seem like John Carmack has plans to slow down any time soon.