Today Facebook Messenger for Android has received an additional feature - support for SMS. You'll be able to send and receive SMS text messages from the app, provided you first set it up as your default SMS app. This is easily done though, and once you turn the feature on your Facebook Messenger communications will remain blue, while SMS messages will show up in purple. The point of this is for you to have to use one less app, at least that's what Facebook seems to think. If you move your SMS use into Messenger, then there's no reason for using another app dedicated to SMS...
Source: http://www.gsmarena.com/facebook_messenger_for_android_now_supports_sms-news-18823.php
