There is a grey area here of calls from businesses which the customer is signed up to, or has had previous dealings with. Many will be unsolicited but not all will be. Many of these calls are coming out of the Third World countries which are barely regulated in this regard, so good luck with enforcing it.
I've been getting a barage of non-stop harassment via unwanted magazine subscriptions. People Inc claims some company called "Subco" signed me up and won't allow me to cancel, only "Subco" can do that. "Subco" then claims they got my information from someone else down the line. They then blame someone else, someone else...
... and I still have no clue who the hell decided to sign me up for 20 magazines in the mail.