This appears to be a reaction to Google Hangouts more than anything else. From the Play Store description for Facebook Messenger, it sounds like you can indeed send messages to friends based on their phone number, but it does not appear to be via SMS. It's more similar to something like Snapchat, where it uses your phonebook to find people who have registered their phone numbers with the app.<p>Furthermore, last week, information leaked regarding Facebook dropping SMS support due to lack of uptake. One source for this: <a href="http://thenextweb.com/apps/2013/10/29/facebook-testing-new-messenger-app-android-drops-sms-support/" rel="nofollow">http://thenextweb.com/apps/2013/10/29/facebook-testing-new-m...</a><p>Long story short, this appears to be a data-only messaging app, not unlike pre-SMS Hangouts or some of the other apps people in this thread have mentioned (Kik, Whatsapp, etc.).