In reply to JJL: Ah, sorry, can't help you with that. I know that Macs have a text-to-speech function but it's not something I'd want to use while driving.
Android devices can use Google text-to-speech but even that's not very driver-friendly. I know there is an Android app called Jarvis that will read texts out when they arrive, and in theory you can dictate texts back that it will send (though I've never found in-car voice recognition to be very reliable).
None of which is any help to you, but it might bump your question so someone who does have an answer can spot it!