As you can tell from the post by XM (9 Aug 2008), XM radio operates by the same rules as organized crime: "we harrass until you buy."
Legally, they must abide by their own do-not-call policy, which is here: http://www.xmradio.com/about/do_not_call.xmc However, they don't. The calls are fully automated and cost them nothing. Enforcement options are few. As a result, they have no motivation to stop. You have to motivate them. Here's how: 1) Make your legal request by calling 800-967-2346
(help & support). Ignore the automated menu. Press 0 to get a representative. Be polite; it's not that person's fault that XM sucks. If you want legal proof of your request, make it by certified letter as well. 2) When they don't stop calling (and they won't), YOU start calling THEM. Yes, call the 888 number. Be sure to always call from the same number that they called when they harassed you that day. Program it into your auto dialer. Every day that they call you, you call them back as many times as you can. Wait for a person to come on line and answer their hello. Then set the phone down and walk away. Or, play with them a bit, or don't even bother to wait. In fact, the more you mix it up, the better, because it will be harder for them to distinguish between a genuine sales prospect and you fighting back.
Why does this work? Because now it costs them money. Before, they felt they had nothing to lose by calling you daily. But if you keep calling back, it costs them money each time someone answers your call.
Because of their harassment, I will never, ever subscribe to XM. Why would I want a relationship with a company that has a policy of disrespecting, bullying, and harassing me? Thankfully, XM is going bankrupt. Meanwhile, I hope the ideas here help you fight back! This is what finally worked for me. Polite requests did not.