3 min read
Two kinds of numbers
A mobile number belongs to a carrier and lives on a SIM. A VoIP number lives on internet phone services and is cheap to create in bulk — which is exactly why many apps block them.
How apps tell the difference
Before sending a code, apps look the number up in carrier databases that say which network owns it and what type it is. If the answer is “VoIP”, many sign-up forms stop there.
What that means for you
- Prefer mobile numbers for messaging, social and AI apps
- If an app says the number is invalid, it’s usually this check — cancel for a refund and try another country
- Free public number sites are almost always blocked: hundreds of people used the same number before you