You can also do this using NFC. Not sure if this is possible with Tasker, but (for example) you could have a car dock with a passive NFC tag (very cheap) on it that would change the phone to automatically read your text messages out loud and prompt you to respond with voice input.

I use NFC Task Launcher to do exactly this.

Link: https://play.google.com/store/apps/details?id=com.jwsoft.nfc...

For my specific car I can detect the Bluetooth connection using tasker, without the need for the NFC chip.

I don't mean to turn this into an, "Isn't Tasker great?" rave, but... isn't it?

This is the concept for the engine, we are glad you "got it." Although you can add it into Tasker too. The bigger picture is that you do not need to be connected to the WiFi or BT radio to enable this.

Handy Profiles did something similar for symbian using cell tower id.