I've read that robocalls cannot be made explicitly illegal because they are protected as free speech, like junk mail.
But that's a bad comparison. Here are some details that might have been overlooked.
1. Fee speech is protected in public spaces and forums like newspapers, etc. and the government operated postal service (you don't get junk mail from UPS or Fedex). My phone is not a public space. A better analogy than a mailbox would be to treat my phone like the front door to my house. It is the front door to my life actually.
2. Door-to-door sales people and church solicitors often knock on my door. I have a nifty tool called a peephole that allows me to determine whether I want to open the door or not.
3. If I put up a fence around my property, they cannot get to my front door without committing the crime of trespassing. Free speech does not protect someone in putting up a loudspeaker in front of my house to broadcast a recorded sales pitch. My phone should fall into that same category. It is harassment, not free speech to have these robots call me day after day after day.
Now, consider this. In a world where automated robots cruise the streets knocking on people's doors and offering to sell them things, as often as two or three times per day, each and every day, (as often as I get calls from robo-callers), how long would this stand before it becomes regulated? How long before enterprising entrepreneurs start offering home defense tools to make the robots go away? How long before we all start putting up fences? I want a fence around my phone.
What we need is not a disingenuous technological solution from a phone company with a conflicted interest. Simply make it illegal to make pre-recorded phone calls that are not pre-approved by the recipient. Make it illegal to obfuscate the caller-ID system and make text-based caller ID mandatory for anything commercial. The technology is already there and this serves the same purpose as the peep hole on my front door. Notice I didn't use the word "spoof". We don't care what the method is, we care what the intention is. If they intend to confuse or deceive us into thinking it's not a pre-recorded call, that's illegal, regardless of the technicalities.
Free speech is still intact because a human can still make the call, just as a human can knock on my door to try and sell me pest control services or soul-saving sermons. But humans are expensive and this will be self limiting. Pre-approved messages, such as appointment reminders for existing appointments (as with a doctor) are exempted from the ban.
With caller-ID and unapproved prerecorded messages laws on the books, with hefty fines for each infraction, the calls will stop. Cell phone and other telephone system call logs are all that's needed to prove the crime. Phone companies already have these records, in abundance. Phone calls are easily traced, even after the fact.
Just make them illegal. There are already limitations to free speech. Extending your commercial messages into my private space should be one of them. Just imagine how you'd feel if every window in your house became a TV commercial, because you know, it's not impossible to project an image from across town onto your windows. Is that free speech? Perhaps, but it's also an intrusion into my personal, private space. A phone is my personal, private space. Free speech does not apply there.