SMS verification

1. Number entry. The user enters a number, usually normalized to E.164 format (for example +44 7700 900123).
2. Screening. Many services look up the number first — line type, carrier, country, sometimes an HLR lookup — and may refuse numbers they consider risky.
3. Sending. A code is generated and sent as A2P SMS through an SMS gateway, often from a short code or sender ID.
4. Confirmation. The user types the code; the service checks it and marks the number as verified.

What it proves is narrow: someone could receive a text on that number at that time. It does not prove identity by itself.

• Friction against mass sign-ups. Real mobile numbers cost money and time to obtain, which slows down automated account creation.
• Account recovery. A verified number gives the user a way back in.
• Reachability. Security alerts and login codes can be sent later.

Because the goal is to limit abuse, each service decides which numbers and countries it supports. A common outcome is that VoIP and landline numbers are refused while real mobile numbers are allowed — see why apps reject phone numbers.

Legitimate causes include: a typo or wrong country code, the service not supporting that number type or country, carrier filtering, rate limits after repeated requests, or temporary gateway delays. Wait for the resend timer, check the number format, and avoid requesting many codes quickly. This guide covers the fixes in detail.

For a one-off verification, a PhoneBorn OTP number receives one code for one service; if no code arrives within the order window, the order expires and is refunded to the wallet automatically. For accounts that will need codes again, a phone-number plan keeps the same number while you renew.