Not all phone numbers are equal. Understanding the difference between VOIP, mobile, and landline numbers helps you make better fraud prevention decisions.
Mobile Numbers
Mobile numbers are issued by cellular carriers (AT&T, Verizon, T-Mobile, etc.) and tied to physical SIM cards. They require identity verification in most countries, making them harder to obtain anonymously. Mobile numbers are the lowest risk for fraud, though they can still be used for fraud via prepaid SIMs.
VOIP Numbers
VOIP (Voice over IP) numbers operate over the internet rather than cellular networks. Services like Google Voice, Skype, and business phone systems use VOIP. Some VOIP numbers are legitimate (business lines), while others are easily obtained anonymously (Google Voice with just an email). VOIP numbers are higher risk but shouldn't be universally blocked.
Landline Numbers
Traditional landline numbers are tied to physical addresses and are difficult to use for SMS verification (they can't receive texts). Some services offer landline-to-SMS conversion, which should be treated as VOIP. Landlines are generally low risk but unusual for personal account signups.
Detection Challenges
Carrier type detection works by analyzing number ranges and querying carrier databases. However, number porting complicates detection—a mobile number can be ported to VOIP and vice versa. Real-time carrier lookups (HLR) provide the most accurate carrier information but add cost and latency.