I used volkerize and searched TM.
There's more than one answer. Here's one from Dec '12
DouglasR | December 16, 2012 I heard from my Ownership Experience Advocate on this issue. I think his answer is of general interest:
"Rest assured, that you will have a Slacker account and access soon enough. We are currently transitioning from a manual to automatic sign-in system. In the coming days or weeks your account information will be pushed to your Model S directly and no further action is required on your end."
Another:
pilotSteve | December 19, 2012 @DouglasR - yup this is exactly the email answer I received. Sounds like there are LOTS of cars (Sigs) delivered without Slacker activated.
I asked "will the login come to my email?" and they said "no, it will be remotely activated by Tesla".
Waiting.......
Here's another try it
tvntesla | December 20, 2012 Slacker account information was pushed into my car by Tesla today and it is working great. If you have tried to use your own free account and it doesn't work in the car, you should log out then click on the T symbol on the top bar, Tesla says, and account information will be pushed to populate the Slacker app. That worked for me. My experience with Tesla service has been great
DouglasR | December 20, 2012 Yep, mine works too! Sweet.
Flag as inappropriate pilotSteve | December 20, 2012
me too.... Slacker activated automatically by Tesla yesterday. Having fun listening to Christmas music and playing 'stump the DJ'. Very nice feature!
Let us know.