Definition
VoIP (Voice over IP)
A phone line that routes calls over the internet rather than traditional telephone infrastructure.
VoIP numbers are cheap and available in bulk, which makes them popular for legitimate business use — and for fraud. Because they're easy to acquire programmatically, VoIP is a common signal in disposable numbers and account-farming schemes.
VoIP isn't inherently bad, so the right move is to treat it as a risk input rather than an automatic block, and to reserve extra verification for VoIP numbers that also look disposable or high-risk.