Why OpenAI & WhatsApp Block Virtual Numbers (And How Non-VoIP Verification Works)

When creating accounts on popular platforms such as OpenAI, WhatsApp Business, Google, or Telegram, users may frequently encounter errors like "OpenAI services are not available for this phone number" or "This phone number cannot be used for verification." These issues arise even when using numbers from well-known providers like Google Voice, TextNow, or standard Twilio virtual numbers.

This article delves into the reasons behind these errors and explains why physical Non-VoIP carrier SIMs are required for successful verification.

The reason for these errors lies in the way modern authentication systems detect virtual lines. When a user inputs a phone number on a web platform, the verification engine sends a request to a Carrier Lookup API in real-time before sending an SMS. These lookup APIs provide metadata about the number, including the country code, phone number, and carrier details.

For example, the JSON response might look like this: { "country_code": "US", "phone_number": "+1XXXXXXXXXX", "carrier": { "name": "Bandwidth.com / Google Voice", "type": "voip" } }.

By examining the carrier type, the verification system can determine if the number is a VoIP line or a physical Non-VoIP carrier SIM. VoIP (Voice over Internet Protocol) numbers, such as those provided by Google Voice or Twilio, are not supported for verification purposes. This restriction exists because VoIP numbers are not tied to physical SIM cards and can be easily obtained without a genuine phone line, making them less reliable for authenticating users.