Not sure of your knowledge on this but I use it a lot, so here's what I know:
- The "Messages" button will only appear AFTER connecting a compatible phone via Bluetooth. After connecting your phone via BT make sure to accept the prompt on your phone that says Chavy Cruze wants to access your messages. If you didn't get this prompt, or forget if you hit yes, just unpair the device and re-pair it.
- Once the Messages menu item becomes available you can sort it to your homescreen if you like. Note that immediately after starting your car it will not appear until the BT starts communicating, usually in about 20 seconds.
- You can't truly text, the MyLink simply offers a list of canned responses. Yes, No, Be there in 10, I'm driving can't text call me, things like that. The sent message will include a signature line "Sent from Chevrolet Cruze"
- You can dictate a text message, but this is NOT part of MyLink, you would dictate to your phone just like you normally would. Note that you may need your radio in the BT audio mode (not FM, CD, etc) because that's where you're phone is listening for you.
Anyways, as to compatibility with a Galaxy S4, I assume it would work, it's a new enough phone. I've had an HTC One S, HTC One M7, and HTC One M8 paired to the car and they've all worked perfectly.