Glossary
What is a VoIP number, and why do fraud teams flag them?
A VoIP number is a phone number issued by an internet-based calling service such as a softphone or virtual number provider, rather than by a mobile network operator through a physical SIM. It can send and receive calls and texts like a normal number, but it is far cheaper and faster to obtain in bulk, which is why fraud teams flag VoIP numbers for extra scrutiny at sign-up and other high-value moments.
How a VoIP number differs from a mobile number
A mobile number is tied to a physical SIM issued by a carrier after some form of identity or payment check, and getting a large batch of them is slow and costly. A VoIP number is provisioned in software: many providers let a user generate a working number in minutes, often for a few pence, sometimes for free during a trial period. Telebase's number type detection distinguishes the two by returning a numberType field of mobile, landline, fixedVoip or nonFixedVoip for any number queried.
Fixed VoIP numbers are usually tied to a physical address, similar to a landline delivered over internet infrastructure. Non-fixed VoIP numbers have no such tie and can be provisioned from anywhere, which is the category that correlates most strongly with abuse.
Why fraud teams treat VoIP numbers as higher risk
A VoIP number is not inherently fraudulent, plenty of legitimate businesses and remote workers use them, but the economics make them the tool of choice for anyone trying to create many accounts quickly. The same properties that make VoIP numbers convenient for legitimate use, low cost, fast provisioning, no physical SIM, make them equally convenient for:
- Multi-accounting: creating dozens or hundreds of accounts to claim sign-up bonuses or promo credit repeatedly
- OTP relay abuse: using disposable numbers to receive one-time passcodes for accounts that require phone verification, then discarding the number
- Identity obfuscation: distancing a fraudulent account from a traceable physical line
Flagging a VoIP number is not a block decision on its own; it is a reason to apply a proportionate extra step, such as a secondary verification method or a lower initial transaction limit, rather than an automatic rejection.
Detecting VoIP numbers at the point of sign-up
A single API call returns the numberType field before an account is created, letting a fraud team route mobile numbers through standard onboarding and route VoIP or landline numbers to a stricter path. This is the same logic used for promo abuse screening; see how it applies in practice on the blocking disposable numbers at sign-up page.