Interestingly, SMS in Messenger doesn't support just text and images. It also supports rich content like stickers, GIFs, emojis and location sharing -- just like regular Messenger conversations. Facebook also wanted to clarify that none of the messages are stored on the company's servers; all of the text messages are sent via SMS as per usual. That does mean that regular texting fees do apply.

This feature is only for the Android app due to the limitations of iOS. But seeing as Apple's own Messaging is getting a lot of these Messenger-like enhancements -- emojis, stickers etc -- iPhone users probably aren't missing out too much.