If you're constantly switching between Facebook Messenger and text message conversations, Facebook is making your life a little bit easier. Facebook Messenger for Android can now send and receive both SMS and MMS messages alongside Facebook conversations, and you can set it as your default SMS application.
Today we are enabling people to use SMS in Messenger for Android to communicate with their family, friends and phone contacts. What this means is you will now have the choice to be able to send and receive your SMS/texts in Messenger and will not have go to different screens on your phone to communicate.
To activate SMS in Facebook Messenger, open the app, then tap the Settings icon in the top right corner. Choose SMS from the list, then turn on "Default SMS app" when you see the option.
Facebook Messenger differentiates between your SMS and Facebook conversations with color, SMS being purple, while Facebook messages will be blue. Facebook notes that Messenger won't collect or store any of your SMS conversations or data on its own servers.
SMS capability should be rolling out to all Messenger users soon.