L_S, it may not be such a simple question after all.
I have Sirius in my Durango, but it is not yet activated. It gets one channel repeating a little "call sirius to activate message".
I was just reading the book, and to activate, you turn the radio on, call them, give them the unique electronic serial number of your receiver, and they activate your radio from their end, either month to month, yearly, or lifetime plans are available.
If you get the cars new, it would seem that the sat company and factory may be doing something promotional. If you get the cars used, maybe the prior fleet owner had them, and there was time left on the plan when you got them.
Of course, there still remains the possibility that there are pirating type internal modifications that are activating the receiver, but much like cable TV decoders and sat TV receiver cards, I think they would be more widely known about by the general public.
Anyone else ??