I had issues with the bluetooth messaging on my 16 LE at first. I eventually had the truck "forget" my iphone and my iphone "forget" the truck. I then restablished a new bluetooth connection and have had zero problems with Siri Hands Free or Entune Messages.
1. Go into bluetooth settings in Entune, and delete your phone
2. Go into bluetooth settings in iPhone, and click on the 4Runner, then select "forget this device"
3. Wait a minute
4. Go back into bluetooth settings in Entune, add a new device
5. Go back into bluetooth settings in iPhone, connect to 4Runner
You should be all set from there. It is also helpful to sometimes have your phone unlocked when you first turn your truck on. Your phone can lock after the truck is turned on (doesn't have to stay unlocked the whole time), but I do that every time and have never had issues.
As discussed previously, to text via Siri in your truck, make sure Siri is enabled. In the iPhone settings, go to Siri, select Siri at top, then select "Access on Lock Screen". Then hold down the "Answer Phone" button on the steering wheel. After 2-3 seconds, the Entune display will show a microphone and you'll hear the Siri "ding ding" sound. Tell her what you'd like her to do ("Siri, text my mom that I love her" or "Siri, play my Celine Dion Greatest Hits Album"). Siri will respond and do exactly what you ask for, assuming she/he is capable.
I have had zero issues with Entune message receiving (Entune reading texts for me) or texting via Siri in my 16 LE since I followed the above steps. Hope it works for you.