Ok, so my wife and I are planning to order in the near future (Model S 60), but we just realized that XM requires the high fidelity audio package and the pano roof. As neither of these options interested me in the first place, I'm not willing to shell out an extra $4K just for satellite radio. How is Slacker as a replacement to XM? Does it cache music so that if you lose cellular connectivity it will continue to play? If so, how long does that last? I've also seen that the car comes with 3G service for 4 years, but I've also seen a thread about an LTE upgrade. Is this now standard on new models or is it still a custom upgrade at a service center? Thanks!