Will not pass muster with FCC. Know Your Customer regulations require the company to … know the customer. They will not last.
Which KYC regulations exist for carriers? AFAIK you can walk into any store and get a SIM card. The most they ask for is maybe E911 which they don't check.
What kind of measures are possible to prevent fraudulent calls when the caller is your anonymous customer? The answer is obviously "none," unless you respond to every complaint by terminating service of the offending customer and hoping they don't come back.
Presumably some fairly basic heuristics would be sufficient. Robocalling isn't economically viable if you only get a few calls per subscription. You need to place (I assume) at least thousands of calls per day per subscription for it to even begin to make sense. Any account doing that is going to be blindingly obvious provided you have even 30 minutes worth of logs.
I can already walk into Walmart and purchase a cheap prepaid device with cash. That's pretty close to anonymous.
You can sign up for US mobile service, which is a Verizon MVNO, right this moment with no personally identifiable information at all.
Remember: neither the visa nor MasterCard payment networks have any support for customer name. Everyone pretends that they do, but they do not. In the absence of an additional security layer like “verified by visa “there is no way to verify cardholder name.
(I literally put 123 Fake St in payment portals.)
Domestically you can buy a Tmobile or Cricket with a pre-paid visa cash card and a gmail address (no ID required), but they won't work outside the US.