There is an announcement up that Second Life’s ™ voice system will be offline for maintenance June 24th (Tuesday) from 12AM PDT. There is no ETA for its return.
See the Grid Status page:
[Posted 3:24 AM PDT, 23 June 2014] Our voice provider will be undergoing scheduled maintenance on Tuesday, June 24th beginning at 12:00 AM PDT. Residents may lose voice access during this time. Once the maintenance is complete, some residents may need to relog to return to voice. Please continue to check this blog for updates.