Facebook Messenger Now Supports Voice Calling for U.S. Accounts: To access voice calling, open the Facebook Messenger app, open a chat with someone, and click the 'i' button in the top right corner. If the feature has been activated -- and the other user also has Facebook Messenger for iOS installed -- there should be a "Free Call" button. If it's greyed out, try tapping it anyway. Facebook is rolling out the feature to all users over the next several days.