A VoIP number (voice over IP) is a phone number served over the internet by apps and online providers rather than by a mobile SIM or a landline.
Why they matter for signups
VoIP numbers can be created instantly and cheaply, often in bulk, which makes them popular for receiving SMS verification codes on fake accounts. Many legitimate people and businesses use them too.
Veqen flags numbers in VoIP ranges with voip_number (impact 50, so review). Some countries have dedicated VoIP ranges (like +44 56 in the UK); in others, like the US, VoIP numbers can't be told apart from ordinary ones by the number alone.