Yes, Vanguard will support voice communication—participating in voice or group communication will be completely optional.
Source: Official FAQ
We are unlikely to have any form of baked in voice support when we ship (bordering on 100% certainty at this point) and there are currently no plans to build our own solution. As we've said all along, we expect people to use 3rd party solutions - if they want to use voice at all. - September 2005
I want to reiterate that voice won't be rolled into the game at launch, and isn't planned in the foreseeable future. That being said, we do expect a lot of people to use 3rd party voice apps - but at the same time, we're not relying on it - so nothing about the game experience will require it. - 31 October 2005