American Airlines now offers free inflight messaging on ViaSat-equipped aircraft using Facebook Messenger (and Messenger Kids). That means it’s offered on all American Airlines Boeing 737’s (including 737 MAXs), Airbus A321s, and legacy American A319s.
Legacy US Airways A319s and Airbus A320s have Gogo internet and are not included. Widebody planes with Panasonic internet are not included.