They’d have to change the laws first. Given that there’s a per-minute cost associated with cell phones (at least historically, even if most people now have unlimited or close enough to it on their plans) for received calls, it’s illegal in most, if not all, places to make telemarketing calls to cell phones.
It may be illegal (in most, if not all places)...but trust me, it happens.
Maybe it’s illegal, but that hasn’t stopped them. I’m signed up for state and Federal Do-not-call lists, and they seem less effective with each passing year.