So is literally every phone number in the US for the past ten years. SIP replaced traditional trunking completely a decade ago. Cellphones have been using digital backend since 3G (though the voice transmission was still analog, for some value of analog)

There is a difference between a number managed by a traditional carrier using VOIP and a number from a free/low cost VOIP provider, especially when you are using text verification as a anti-spam measure.

>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...

I also switched from Voice to Fi and it's technically a VoIP number transferred to the Fi MVNO... Not sure why that fails the VoIP test, I'm paying for normal phone service but it's not legit enough???

I'm not sure how one validates whether a VoIP number is being used for VoIP vs as a "real" phone number but this seems like a curious edge case.