This feature should be rolling out to everyone. There you can pin up to 3 different conversations to the top. Keeping in mind how many new conversations you might be getting to verify your phone number, this feature can be really useful.
How to test:
- Open the main screen.
- Long press on any of your conversations.
- Tap on the Pin icon on top.
Via XDA
Messages - Apps on Google Play
Simple, helpful messaging by Google
