Voice over IP is now available in IOQuake3 and there are no conflicts with the vanilla Quake 3 engine. The support for it is there at the core, but it hasn’t been polished out completely due to concerns of compatibility, as stated above. For this reason, it is difficult to create a User Interface for the settings, but this could be left to individiual mod or game developers.

There are still things worth doing: adding a real UI (including
controls, config menus, VoIP field in the server browser, a real
recording meter, and displays of who is saying what), blacklist support,
recording support outside OpenAL, fix audio streams when saving a demo
to an AVI, figure out where that echo is coming from, positional audio,
"QuakeRadio", etc...I don't think I'll have time to work on any of these
in the near future, but I'm happy to advise any volunteers that want to
take a shot at them.

Of the many things that Icculus included in his final patches include:

documentation in voip-readme.txt (anyone can feel
free to improve or reformat that, if they like), a cheesy VoIP meter to
show how well the game "hears" you when recording (best I could do
without changing the UI or cgame code: +set cl_voipShowMeter 1), and
support for transmitting to just the people in your crosshair or the
last person that attacked you (+set cl_voipSendTarget "crosshair" or
"attacker").

He also included a scrolling credits screen (Product of him trying to familiarize himself with the Q3 UI) which so rightly credits the great developers and maintainers of the engine.

I just committed a patch to SVN from Hobbes for Slackware SlackBuild support, thank you Hobbes!