Why services reject VoIP numbers
If a sign-up says “this phone number cannot be used for verification”, it has almost always recognised the number as VoIP rather than mobile.
How the check works
Numbers are allocated in blocks, and public numbering databases record which block belongs to which carrier and of what type. A lookup against that data returns the line type in milliseconds, long before any SMS is sent.
That is why the rejection is instant: nothing was ever sent to the number.
Why platforms bother
Free or near-free numbers make fake accounts free to produce. Blocking the ranges those numbers come from is the cheapest fraud control available, and it costs almost no legitimate users — very few people verify with a VoIP line.
What gets through
Mobile numbers on real carriers. Not because they evade the check, but because they pass it — they are the exact thing the check is looking for.
- Google Voice and similar services: blocked nearly everywhere
- Landlines: rejected by anything requiring SMS
- Mobile numbers: accepted, subject to the platform's own reuse limits
