If you are in the Beta stream of Facebook Messenger for Android, you can now activate the option for SMS in Android's 'default application' settings. Seems quite stable, I like having the chat heads for SMS too :)
They took the feature away for the past year or so, they just added it back now.
I'm pretty sure it always seemed to ask me every time I install the messenger app on a new phone, if I want to use it for SMS too? Or am I interpreting their message wrong?
Thought this feature was very old. I have been using this for alert notification on my phone since Feb 2015
thanks for heads up!!! i loved this feature, thought the chat heads were brilliant and no other SMS app I tried was as good. I was so annoyed when they took this away.
I just opened messenger for the first time in ages (not in beta), opening message stated SMS is now supported. So yeah I didnt have to do anything but open messenger.