I haven‘t tried it, but I‘m willing to bet that at least one of these would claim that my primary phone number "is not a mobile phone number" (but I use it on a phone), "is not registered in my name" (it is, and how do you claim to know?), or "is a VoIP number, which is insecure and therefore not allowed".
Phone numbers are neither good user identifiers nor viable authentication factors.
We do not verify any of your personal information. We neither have access to that nor store any of it on our system. Our PhoneCheck product simply returns a true or false. Is your phone number tied to this SIM Card. This is information the MNO already has, they know your phone number and your SIM Card. The request is made over a cellular data connection from your device to the MNO
What's the difference between these three tiers of authentication, then? And what makes it different from SMS-OTP (leaving aside SS7 security concerns and focusing on SIM swapping, which I believe is responsible for the majority of successful attacks so far)?
It's actually comparable to SMS OTP delivery in most countries. (Only the US and a few other "shared cost" countries offer inbound SMS delivery for sub-cent amounts; in the EU and other "sender pays" countries, mid-single cent amounts are the norm.)
That still doesn't make using a phone number a good authentication or identification value, though.
Note that I wrote "most countries other than the US".
Your first reference seems to be US only; the second one lists around 2-10 cent per message to most non-US destinations.
Since this is based on what phone networks charge these service providers and other networks for inbound SMS, anything much cheaper than that is usually using unreliable SIM farms or even more dubious means of message delivery (like hijacked Android smartphones on unlimited messaging plans used without the owner's explicit consent).
Viewed globally, cheap and reliable outbound SMS are a US-specific anomaly.
For thouse countries, typically with lower standards of living, their pricing will be even more prohibitive! There are tricks like callbacks, etc. to deal with expensive texting and many services use those already!
Let's not get into the debate about standards of living in the EU vs. the US, but doesn't all of this outline my original point, i.e. 3-9 cents per authentication being pretty on par with what companies seem to already be willing to pay for two-factor authentication (via SMS-OTP) globally?
Phone numbers are neither good user identifiers nor viable authentication factors.