The service is initially available in Belgium, Canada, Croatia, Denmark, France, Greece, Ireland, Laos, Lithuania, Mexico, Nigeria, Norway, Oman, Poland, Portugal, the UK, the US and Uruguay.
http://newsroom.fb.com/news/2015/04/introducing-video-calling-in-messenger/
- Last week, Facebook disclosed that it served 936 million daily active users (DAUs) on average for March 2015, an increase of 17% year-over-year. Mobile DAUs were 798 million on average for March 2015, an increase of 31% year-over-year. Monthly active users (MAUs) were 1.44 billion as of March 31, 2015, an increase of 13% year-over-year. Mobile MAUs were 1.25 billion as of March 31, 2015, an increase of 24% year-over-year.