Mark Reins was quoted a few days ago saying that the Xbox 360 version of Unreal Tournament III (Xbox 360, PlayStation 3, PC) hasn't started production yet. He clarifies on this position saying that the developers will get back to Xbox 360 version as soon as they finish their "efforts on shipping the various PC and PS3 versions" and taking some time to enjoy the holidays.

He also says that the game can already played on the Xbox 360 but still needs a "decent bit" of work, like implementing Xbox Live into the game and how Microsoft can accommodate mods:

We had the game up and running on all three platforms up until last spring. In fact Official Xbox Magazine came out and played the game for a great cover story they did on it.

There's still a decent bit of work to do. For example we have simple LAN play but no Xbox Live implementation yet and we need to work with Microsoft to figure out how to accommodate mods on their platform.

Via Joystiq