Not all phone numbers are equal. Mobile numbers can receive SMS, landlines typically cannot, and VoIP numbers may indicate fraud risk. Understanding line types helps you optimize SMS delivery, detect potential fraud, and improve user experience.
Mobile Numbers
Mobile (cell) numbers are assigned to wireless devices. They can receive both calls and SMS messages. For two-factor authentication and OTP delivery, mobile numbers are ideal. In most countries, mobile numbers have distinct prefixes or number ranges that identify them as mobile.
Landline Numbers
Landlines are traditional wired phone connections. They can receive calls but typically cannot receive SMS (though some carriers offer text-to-landline services). If your application relies on SMS verification, you should either reject landlines or offer a voice call alternative.
VoIP Numbers
Voice over IP numbers (like Google Voice, Skype numbers) route through the internet rather than traditional phone networks. They can receive SMS, but are often flagged as higher fraud risk because they're easier to obtain anonymously. Some services block or require additional verification for VoIP numbers.