True, but I would have the right to prevent people from coming onto my property to use my well to extract water from the watertable. Similarly, I have a right to prevent telemarketers from using my phone equipment for their business. They're free to use their own phone lines and the phone company's lines for their business, but they can't use my property if I've posted the electronic "do not trespass" sign.
When was the last time a telemarket came onto your property? Telephone conversations are a wave phenomenon. It's like owning half a lake. You can keep the fellow off your half of the lake, but you can't stop him from making those little ripples that wash up on your beach when he dives in on his property. Neither can you use the fact that you don't like those waves to make him stop swimming in his water.
What do you want to bet you never had a telemarket step onto your property?
Yes, you can disconnect you phone or turn it off. If they have no right to affect how you chose to use your equipment in your home, you have no right to affect how they use their equipment in their business. You have the right to hand that do not call sign, and it's turning off the phone.