Slacker Premium (it's now called LiveOne) is $9.99 per month (USA) paid separately. This will give you your own login and password that you can use in your Tesla and any of your supported streaming devices.
I have mine billed through Apple and listen to it on my phone and in my car. I also pay the Tesla Premium Connectivity annually for $99. But now that Tesla is supporting Apple Music I might just move all my playlists to Apple Music and cancel the Slacker/LiveOne subscription.