My son bought a Sirius capable system for his car off eBay. It was brand new, in the box, never used. He hooked it up about 10 months ago, flipped it on and it worked from get the get go.
Now isn't it supposed to be registered somehow? He's used it 10 months, never registered it, has never been billed for the service and continues to use it.
Down side, on clouded days or while riding tree lined streets, the service isn't so hot. I surmise the service is a lot like Dish or Direct TV satelilites, sketchy service on bad weather days.