Linden Lab has announced that it is currently averaging one billion voice-minutes per month. That's time actively engaged in a voice session, not just time spent with voice support enabled. That's quite a statistic. That puts Second Life's voice service right up there among the top VoIP providers, and around 12% of Skype. That's very impressive.
In the 18 months since voice was introduced, roughly 15 billion voice-minutes have been served, through Vivox's voice services for Second Life. Additionally there are new products/services. Some available from today, and some scheduled for later this year.