To have Siri read your text messages automatically, you'll need to be wearing second-generation AirPods, AirPods Pro, Powerbeats Pro, or Beats Solo Pro headphones. To set up the feature, go to your iPhone's Settings, then tap Notifications and toggle on Announce Messages with Siri. When you get a new message, Siri will make a sound, then read who the message is from and the message's contents.