When developing, testing, or signing up for modern platforms like OpenAI (ChatGPT), WhatsApp Business, Google, or Telegram, you have likely encountered these frustrating errors:
⚠️
"OpenAI services are not available for this phone number."
⚠️"This phone number cannot be used for verification."
⚠️"Virtual phone numbers (VoIP) are not supported."
Why do these errors happen even if you use numbers from popular providers like Google Voice, TextNow, or standard Twilio virtual numbers?
In this post, let's explore how modern authentication systems detect virtual lines and why physical Non-VoIP carrier SIMs are required.
When you enter a phone number on a modern web platform, the backend verification engine queries a Carrier Lookup API (e.g., Telesign, Twilio Lookup, or Neustar) in real-time before sending the SMS.
These lookup APIs return metadata about the number:
json
{
"country_code": "US",
"phone_number": "+1XXXXXXXXXX",
"carrier": {
"name": "Bandwidth.com / Google Voice",
"type": "voip"
}
}