The iPhone version of the Facebook Messenger app has just received an update today that would turn it into a universal app, and hence, compatible with the iPad. Apart from that, this version 7.0 update will come along with a tweak which allows you to place calls in a more reliable manner, not to mention a bug fix that will load all of your active Facebook friends in a far faster manner than ever before.
Do expect everything that ran on your iPhone previously to also work just nice on your iPad with this particular update, where it will include the likes of stickers, group conversations, voice messages, location sharing, and free calling, among others. Better late than never is the principle here, especially with false alarms that hail all the way from the beginning of 2013.