In the upcoming patch we will be introducing voice chat, which allows players to talk to each other in-game with the use of a microphone. To ensure that we provide the quality play experience we’re committed to, we will be ramping up the voice chat feature in multiple stages. Currently we are scheduling voice chat to be available on patch day for a limited number of realms. While all realms will still receive the 2.2 patch, and all the content and changes therein, only some realms will have voice chat enabled at the start. We plan to then enable voice chat for the remaining realms the following week. This ramp up release will help us to test the voice chat feature in a live realm environment before enabling it on all realms.

To read more about the upcoming Voice Chat feature, click here:
https://forums.worldofwarcraft.com/thread.html?topicId=1272012664&sid=1

The initial set of realms that will have voice chat enabled on patch day:

Aerie Peak
Altar of Storms
Alterac Mountains
Andorhal
Anetheron
Anvilmar
Archimonde
Arygos
Black Dragonflight
Blackwing Lair
Dalaran
Dalvengyr
Deathwing
Demon Soul		 Dentarg
Doomhammer
Duskwood
Executus
Gnomeregan
Haomarush
Icecrown
Jaedenar
Kel’Thuzad
Khadgar
Lethon
Mal’Ganis
Norgannon		 Onyxia
Scilla
Sentinels
Steamwheedle Cartel
Tanaris
The Venture Co
Thrall
Turalyon
Uldaman
Undermine
Ysera
Ysondre
Zuluhed

All other realms are scheduled to have voice chat enabled the week following the patch release week.