The company plans to start testing voice on the "main grid" -- the main Second Life service -- in "the next few weeks," according to a post on the Official Linden Blog.
Kudos to Linden Lab for laying out plans for this major upgrade in plain language. The timetable is vague and general, but that's OK -- software and Internet service development usually doesn't keep to a schedule. It's ready when it's ready.
This is exactly the kind of behavior that I said yesterday Linden Lab needs to do more of. Keep it up, guys!