A VoIP number lookup (line type lookup) tells you whether a phone number is mobile, landline, fixed VoIP, non-fixed VoIP, toll-free or premium, using numbering plan data, carrier databases and portability records. Businesses use it at sign-up and before sending OTPs to cut fake accounts and SMS fraud, and to route messages and calls correctly.
What is a line type lookup?
A line type lookup takes a number in E.164 format and returns its type and, usually, its current carrier. The common categories are:
| Line type | What it means | Typical use in checks |
|---|---|---|
| Mobile | Number on a mobile network, tied to a SIM | Normal for SMS OTP |
| Landline (fixed) | Traditional fixed line | Cannot receive most SMS; offer a voice OTP instead |
| Fixed VoIP | VoIP service tied to a physical address, often a business line | Usually acceptable, depends on use case |
| Non-fixed VoIP | VoIP number obtainable online without a fixed address | Higher risk for sign-ups and payments |
| Toll-free, premium, shared cost | Special number ranges | Usually rejected for personal accounts; premium ranges are a fraud signal |
How does VoIP number detection work?
Providers combine several sources. The national numbering plan says which ranges were allocated to which operator and for which service. Number portability data shows the current operator if the number was ported (see mobile number portability). For mobile numbers, an HLR lookup can confirm the network and whether the number is active. Commercial databases then classify carriers as mobile, fixed or VoIP. Results are not perfect: some VoIP providers use ranges that look like landlines, and data lags behind new allocations, so treat line type as one risk signal, not a verdict.
Why do apps block VoIP numbers at sign-up?
Because non-fixed VoIP numbers are cheap and quick to obtain in bulk, they are often used to create fake or duplicate accounts, abuse sign-up bonuses and referral rewards, and run spam or scams. Blocking or adding friction for them protects:
- Your SMS budget: fraudsters trigger OTPs to numbers they profit from, see SMS pumping.
- Your users: one person per account makes bans and limits meaningful.
- Payments and promotions: fewer chargebacks and less bonus abuse.
Blocking has a cost: some real users only have a VoIP number, for example business users or people abroad. Many services use a softer path, such as asking for extra verification, a card check or a manual review, rather than a hard block.
Is it a VoIP number? How to use the result
- Validate the format and reject impossible numbers before any lookup.
- Look up line type and carrier at sign-up and when a user changes number.
- Apply a policy per line type and country: allow mobile, review non-fixed VoIP, block premium ranges.
- Combine with other signals: request velocity per IP and device, country mismatch, and sudden bursts to one number range.
- Pick the channel: send SMS to mobiles, offer voice OTP to landlines (see OTP fallback).
The full OTP checklist is in OTP SMS best practices, and the APIs that return these data are compared in phone number validation API.
Is a VoIP number lookup accurate?
Accuracy is good for mobile versus landline in most countries and weaker for the VoIP categories, because the line between fixed VoIP, non-fixed VoIP and normal landlines varies by country and by data source. Ported numbers and newly allocated ranges are the usual errors. Test two providers on a sample of your own traffic before relying on one.
Clean OTP delivery
Line type checks reduce wasted messages; reliable routes do the rest. VoIPMatcher sources A2P SMS routes for OTP traffic from its carriers. Request an OTP SMS route.
Frequently asked questions
What is the difference between fixed and non-fixed VoIP?
A fixed VoIP number is tied to a physical service address, like a business phone line from a cable or VoIP provider. A non-fixed VoIP number can be obtained online without a fixed address and used from any device, which is why risk systems treat it with more caution.
Why does my bank not accept my VoIP number?
Many banks and apps only send verification codes to mobile numbers because non-fixed VoIP numbers are easier to obtain anonymously and are often used in fraud. Contact the service: most offer another way to verify, such as a mobile number, an authenticator app or a branch visit.
Can a line type lookup tell who owns a number?
No. A line type lookup returns technical data such as the number type, current carrier and sometimes whether it is active. It does not return the subscriber's name or address. Caller name data is a separate service with its own rules and consent requirements.
Is a VoIP number lookup free?
Some sites offer a few free checks, but business use usually needs a paid API priced per lookup. Prices depend on the data returned: line type and carrier cost less than a live HLR lookup that confirms whether a mobile number is currently reachable.
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