I just ran into the "this isn't a phone number" issue with Telegram this morning. It claims my Google Voice (well really Project Fi now) number is a VOIP number, so I can't use it :(.
I suspect this is due to the NIST report about using VOIP/SMS for 2-factor was not secure (which is true. They can be spoofed).
I've also worked for a teleco that, in the case of getting an SMS for a ported number, would just send that SMS to ALL the other national providers in that country. We used relays for the other providers that would just drop the message if it didn't belong to them. My first job was actually to fix that by doing a ported number lookup and sending SMSs to only the provider it was ported to.
>We find that miscreants rampantly abuse free VOIP services to circumvent the intended cost of acquiring phone numbers, in effect undermining phone verification. Combined with short lived phone numbers from India and Indonesia that we suspect are tied to human verification farms, this confluence of factors correlates with a market-wide price drop of 30-40% for Google PVA until Google penalized verification from frequently abused carriers
https://static.googleusercontent.com/media/research.google.c...