Is there any support or package for voice chat in a 3d multiuser environment in Unity?
You could use the TS3 SDK. Not sure how much they charge but the quality would be great. Here is the link for more info: http://www.teamspeak.com/?page=teamspeak3sdk
Unity doesn’t come with a built in voice chat. However if you want to make your own there are several libraries available that provide basic voice chat. You won’t get the top quality using many of the library but they are start.
Unity doesn't come with one, and I haven't seen one given out or for sale, but it's definitely possible to make one for Unity Pro (I use one, but unfortunately it's proprietary and not going public)