Note that it's pretty hard to validate a phone number belongs to someone. You could ask their telephone company, but their telephone company shouldn't disclose subscriber information, and even if they did, maybe you get a name, but lots of people have the same name as me, so what does that show?
Commonly, people send a text message with a code or a phone call with a code to demonstrate control (not belonging), but that's almost always automated, and you would need the number to be validated before you could validate it.
But there’s still no way to know if that number later gets released to another person.
Some carriers do make available lists of recycled numbers, and some telephone information companies aggregate these lists, when I was looking, coverage was sparse though, and questions about reliability and privacy were too big relative to the limited coverage. Sharing of confidential information was an issue too: carriers wanted to provide events only for numbers of interest to a 3rd party service, so the carrier didn't divulge the number of customers leaving their service; the 3rd party service didn't want to provide numbers of interest because it would divulge user count. I may be biased (I was working for a service), but the recycled number list feels less privacy invasive than providing numbers of intetest. The numbering space is small, so you can't meaningfully obscure the numbers, etc. Determining which carrier is responsible for a number is also tricky, of course.
Of course, getting a working incoming number for all countries worldwide that doesn't cost users an arm and a leg to message is not exactly easy.
Marks was used as precedent for this lawsuit. Facebook argued that this case was different from Marks. The Ninth Circuit found otherwise. SCOTUS appears to have shot down the ruling from Marks.
Marks was widely regarded as a terrible decision because it made no sense at the time. It's nice to see SCOTUS return some common sense to the law.
Note also that the TCPA allows for statutory damages of up to $1500 per violation, so it takes less than 675 calls/texts to rack up $1M in liability. Class action attorneys love it because they don't have to show damages. They only have to show that the call or text was sent using an autodialer.
Citation? I've looked over _Marks_, and it doesn't seem unreasonable, and the 9th circuit was not the only court to adopt the same interpretation of the statute. I can see why certain industries would lothe that rule, but it doesn't seem to me that the Court's opinion is a fine, if not exemplary, example of legal interpretation. Similarly, it's far from clear that Congress intended that such behavior be permissible when they passed the law.
Honestly, _Marks_ makes more sense to me than the Supreme Court's interpretation does. Reading a law's text in the narrow and formal way that they did causes the law to be nonsensical.
So even if you are sure it is the number of a customer, it is verified and used for correspondence it can still be sometime else number a year (I don’t know how long the recycling waiting time is) later.
There's work being done to address that:
The evidentiary question of whether a customer had actually consented to receive calls/texts from a service to which they had subscribed is separate from the question of liability for using automation to call/text a number that turns out not to belong to a customer.
The other two are fine casualties for a world with far less autodialing. Call centers probably ought not exist.
1) using caller ID to return a missed call unless you were sure you were calling an existing customer
2) sending a one-time password over SMS, unless you had already validated that the telephone number belonged to your customer
3) using call-center software that automatically connects an operator to the customer's on-file telephone number in order to validate that the number was correct!