They're using the number as an identifier for the person behind it. Telesign is integrated into fraud and risk management systems. The clients aren't asking "should we market to this phone number?", they're asking "should we accept the credit card of this e-commerce customer with this billing phone number?". If you have a bad rating, you won't be able to do business with some companies you might want to, like having a bad credit score except nobody has to pull your credit.
To put the shoe on the other foot, if you wanted to create a startup that offered anonymizing VPNs to privacy-conscious techies, and offer a free trial, you'd have a spam/scam problem. That site would be very attractive to a large number of people wanting to do illegal things with it. You could filter a lot of them out by requiring a phone number on signup, verifying ownership of that number, and rejecting registration from any with a low reputation score. People using burner VOIP numbers or the same number to make accounts reported as fraudulent at other businesses would have a low score.
You probably don't want to have a bad reputation if you care about signing up for things online. Like they said, Telesign has a huge number of clients. Lots of other fraud detection systems, like MaxMind's which are recommended occasionally on HN, are built on top of Telesign's APIs as well.
Most burner numbers are for legitimate purposes. It is probably only way to avoid spam. Or other way: I did not gave my phone number to most of my paying customers, why should I give it to some random website?
If you wanted to offer anonymizing VPNs to privacy-conscious techies, and first wanted to verify their identity, isn't that contradicting your own business model?
To put the shoe on the other foot, if you wanted to create a startup that offered anonymizing VPNs to privacy-conscious techies, and offer a free trial, you'd have a spam/scam problem. That site would be very attractive to a large number of people wanting to do illegal things with it. You could filter a lot of them out by requiring a phone number on signup, verifying ownership of that number, and rejecting registration from any with a low reputation score. People using burner VOIP numbers or the same number to make accounts reported as fraudulent at other businesses would have a low score.
You probably don't want to have a bad reputation if you care about signing up for things online. Like they said, Telesign has a huge number of clients. Lots of other fraud detection systems, like MaxMind's which are recommended occasionally on HN, are built on top of Telesign's APIs as well.