I literally JUST got off the phone with XM to cancel my service because the '08 i just bought has the SAT button, but no XM module installed. I called the dealer and he told me that Toyota had discontinued making the module and cant be ordered.
However, I use some specific websites for OEM parts and they are still available there. They want $190 for the module and another $81 for the install kit. You NEED both because I think the install kit comes with certain wiring harnesses. Nickel n' Dime yah every chance they get!