Drysc goes on to say that Voice Chat will be on separate servers from the actual game realms:
Voice chat doesn't run through the game servers. This test is of the voice chat servers themselves, not the game realms. If there's an issue voice chat won't be available, the realms themselves shouldn't be affected. In any case, that's what this initial set of realms is to test, how voice chat handles and interacts with the realms on a wider scale.
I don't know if this means we are getting Patch 2.2 on Tuesday 9/18 or not, but I do know that I won't have Voice Chat to play with on my main realm until the week after its release.
Check out our hands on look at Voice Chat and look for the list of realms getting Voice Chat first after the jump.
The initial set of realms that will have voice chat enabled on patch day:
Altar of Storms
The Venture Co
All other realms are scheduled to have voice chat enabled the week following the patch release week.