I don't actually believe this argument, but I'm curious what self-described free speech absolutists think.
There are some obvious nuances around different media, especially around physical audio in the real world, where just because you're saying something that is reaching people's ears does not within reason mean you're "forcing" them to "hear" it, but in the case of a robocall it's definitely an attempt to force itself on you, especially in light of the Do Not Call list providing positive in-advance affirmation of a lack of desire to hear this particular speech.
I think is one of those cases where a "reasonable person" standard works pretty well and trying to get nitpicky on "but what if...?" is mostly a way to get yourself turned around in circles, not a path to enlightenment.
(If nothing else, you can't have a generalized right to force other people to listen to you out of sheer scale; the many hundreds of thousands of people who would jump on that "right" to do something would consume well in excess of 100% of your time if such a right generally existed, in our current socio-technological landscape in which broadcast is so easy and readily available to everyone. Robocalls are an example of that problem squeezing through even despite our layers of protection; it would be far worse if our society determined there was a right to such things.)
I do not give robots rights. You - or your representative -can personally call anyone you want to. You can have a robot dial the phone even - but you need to be personally on the line when the call connects, not a millisecond latter.
Harassment is illegal so you won't be calling me more than once. Even without a do not call, you won't call more than once unless you can show the call is different from the last time in a significant way. You won't get out of this by starting a different "shell company" to call me again either.
Fraud is also illegal. This stops most instances right there. Note that it is also fraud to take up excessive time, if I've "won a car" I better get a car with not much more than the legal paperwork.
If they can't stop intentionally deceptive businesses that spoof their identity on those shared resources from calling my elderly parents 3 times a day because of freedom of speech, they can go ahead and return a bunch of my property and let me do what I want with my ham radio.
A good analogy would be stopping someone on the street and trying to talk to them. In most cases, you have that right. But the other person also has the right to ignore you.
It sounds like the phone companies won't block without your permission, they will give you (the consumer) the tools to block based on your own criteria.
Social media platforms have different levels of interruption from direct messages depending on whether someone is already your friend. They categorize direct messages from strangers and suspected spammers differently but they usually still provide a section you can check to see them. Gmail does the same with the spam folder.
I could see something like that where you have a separate spam section where you can see a history of who tried to call you but don't get notifications from it.
A system like that would be hard to argue that they are blocking freedom of speech.