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.
By SwiftSMS · Published
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
