It's been mentioned here and there before, but John Carmack confirmed its development in a Doom Classic update.
If there's one thing you could say about John Carmack, it's that he's an interesting read to say the least. On October 30, id Software finally released the iPhone version of Doom Classic. For $6.99, gamers get 36 levels of classic Hell goodness from all four original episodes: Knee-Deep in the Dead, Shores of Hell, Inferno, and Thy Flesh Consumed. The game even provides deathmatch and cooperative play for up to four players via "wireless Internet."
Once the game finally swam past the infamous Apple mad scientists stationed in the App Store, Carmack posted a development overview of the iPhone remake, talking about putting the project aside to work on Doom 4(!) and Rage, or how id software decided to put the game aside so it didn't clash with Doom Resurrection. He even goes into the whole networking issue, revealing how 3G was disappointing and overall caused ping times of 360 ms despite its "speed."
But somewhere in that plethora of gaming goodness, Carmack revealed that the company is indeed working on Quake Classic for the iPhone. "We have two people at Id that are going to be dedicated to iPhone work," he said. "I doubt I will be able to personally open Xcode again for a few months, but I do plan on trying to work out a good touch interface for Quake Classic and the later 6DOF games."
Carmack also said that there may be a free tech demo using the company's idTech 5 megatexture content creation pipeline, and also mentions the Rage themed game in his update as well. "I'm not sure exactly what game I would like to do with it, so it might be a 500 MB free gee-whiz app," he said, referring to the idTech 5 demo. "I want to work on a Rage themed game to coincide with Rage's release, but we don't have a firm direction or team chosen for it. I was very excited about doing a really-designed-for-the-iPhone first person shooter, but at this point I am positive that I don't have the time available for it."
Quake... my favorite game of all time! -kp