Nearly one year ago to the day, Blizzard revealed that it was working on a native, cross-game voice chat feature for its Battle.net client. That feature is now live for everyone although it's taken on a different name (and isn't as flexible as one might hope).
Blizzard announced the new feature, which it is now calling Blizzard Voice, on Twitter. In order to give it a try, you'll simply need to update your Blizzard Launcher to version 1.5.1, Build 8098 or newer. Upon logging in, you'll be greeted with a pop-up explaining that the feature is now available.
From there, navigate to your friends list, select "create a channel" then invite those that you want to chat with into the room. Optionally, you can simply right-click on a friend and select "start a voice chat" for one-on-one conversation.
As PC Gamer notes, Blizzard Voice doesn't allow for system-wide chat. Instead, conversations are limited to friends and friends of friends. While this approach will no doubt reduce the amount of trolling you'll have to put up with, it also essentially negates itself when you jump into a pick-up game with random players as you can't readily communicate.
Blizzard last month announced that it would be doing away with the Battle.net name, hence why the new voice chat system doesn't carry Battle.net branding.