The SMS functionality itself is very basic (think of it like retro Nokia). Just use Baybayin SMS when you want to type or read in baybayin. Use other text messaging apps for a more feature-rich experience.
NOTE: The person receiving the text message must also install Baybayin SMS in order to see the baybayin characters, if they are an Android user. iPhone users with iOS 9.0 and above will be able to see baybayin without any special apps. Tell iPhone users to search for the "Baybayin Keyboard" in the app store if they want to be able to type in baybayin.