Not available in AU either, but someone has uploaded the APK according to the comments of this post http://www.gizmodo.com.au/2011/08/this-is-the-facebook-messe

Not available in AU either, but someone has uploaded the APK according to the comments of this post http://www.gizmodo.com.au/2011/08/this-is-the-facebook-messenger-app-you-cant-get-yet/ http://www.gizmodo.com.au/2011/08/this-is-the-facebook-messe...