Guide · Line types
What is a non-VoIP number, and why won't some services text one?
A non-VoIP number belongs to a mobile line: a number a carrier issued for a phone on a cellular network. A VoIP number comes from an internet phone service. Many services check which kind a number is before they send a verification code, and many refuse the VoIP kind. That check is why a code never arrives on some numbers and lands instantly on others.
By the Cleat team · Updated September 11, 2026
How services tell the difference
Before a business texts you a code, it can pay for a lookup that says what kind of line your number is. Twilio's Line Type Intelligence is one widely used lookup. It returns types such as mobile, landline, fixedVoip and nonFixedVoip, and its documentation gives Google Voice and Enflick, the company behind TextNow, as examples of nonFixedVoip.
01
You enter a number
A bank, app or marketplace asks for a phone number to send a code to.
02
It looks up the line type
A lookup service answers: mobile, landline, fixed VoIP or non-fixed VoIP.
03
It decides
A mobile line gets the code. A service that filters VoIP never sends it.
| Line type | What it is | How services often treat it |
|---|---|---|
| Mobile | A number on a cellular network, issued for a phone or SIM | Accepted by most services that send codes |
| Landline | A fixed phone line | Often refused for text codes |
| Fixed VoIP | An internet phone number tied to a physical phone service | Refused wherever a service filters VoIP |
| Non-fixed VoIP | A virtual number obtained online, such as Google Voice or TextNow | Refused wherever a service filters VoIP |
Twilio's advice to the businesses that use it is to filter before sending: “VoIP numbers are often correlated with bots and don't have the same assurance that you're interacting with a real and unique user” (Twilio).
Why the rules got stricter
Text-message codes are a target for fraud, and so are the people who receive them: the FTC reported $330 million lost to text scams in 2022 (FTC). Security guidance moved too. NIST's digital identity guidelines (SP 800-63B, revision 4) treat codes sent over the phone network as a “restricted” authenticator, and say verifiers “SHOULD consider risk indicators (e.g., device swap, SIM change, number porting, other abnormal behavior)” (NIST). The previous revision was blunter: methods “that do not prove possession of a specific device, such as voice-over-IP (VOIP) or email, SHALL NOT be used” (NIST).
What internet-number providers say themselves
Companies that sell VoIP numbers are open about the limit in their own help pages:
Hushed
“NOT guaranteed to work with third-party verification due to blocks implemented by certain services”
https://support.hushed.com/hc/en-us/articles/360015707631MySudo
“some services do not support VoIP numbers by design”
https://support.mysudo.com/hc/en-us/articles/360019981814Quo (formerly OpenPhone)
“In many cases, services that use 2-factor authentication (2FA) don't allow virtual phone numbers to be used during the registration/verification step”
https://www.quo.com/pricingMultiMFA
“MultiMFA SMS numbers are VoIP numbers. Some platforms reject VoIP numbers”
https://multimfa.com/shared-sms-verification-number
“Non-VoIP” doesn't mean “accepted everywhere”
A mobile line passes the line-type check. It doesn't exempt anyone from a service's other rules: who you are, where you are, your account's history. Most services that turn away VoIP accept a real mobile line. No provider can promise that every service accepts every number, and Cleat doesn't either.
Your options, honestly
- Your own mobile number. It works, but every account then depends on one SIM, and your personal number goes to every site that asks for one.
- A prepaid US SIM or eSIM. A real mobile line. You need a compatible phone or eSIM slot, and some carriers only activate inside the US: Tello's eSIM must be activated while “physically located within the United States” (Tello).
- An authenticator app or a security key. Stronger than text codes. Use one wherever a service offers it; many banks still insist on SMS.
- A dedicated real mobile line delivered online. That's what Cleat is: a US mobile number that receives texts into a web inbox, email, Telegram or your own tools, with one verified owner and no SIM to install. It's receive-only.
- Free “receive SMS online” sites. Public, shared, reused numbers. Anyone can read a code sent to them. Don't use them for anything you care about.
Who this isn't for
Cleat lines are for your own accounts and your team's, and every line has a verified owner. Cleat isn't for running lots of numbers, for accounts in someone else's name, or for a number nobody can trace to you. Why we verify every owner.
Keep reading
Does Google Voice work for verification codes? · Is TextNow VoIP? · A shared 2FA number for teams · A US number for expats and non-residents · Cleat pricing
Questions
Is a non-VoIP number the same as a “real” number?
In practice, yes. People say “real”, “carrier” or “non-VoIP” for a mobile line, and “virtual” or “VoIP” for an internet number.
Is Google Voice a non-VoIP number?
No. Twilio's documentation uses Google Voice as its example of a non-fixed VoIP number. Our guide to Google Voice and verification codes goes further.
Is TextNow non-VoIP?
No. TextNow is an internet phone service, and Enflick, the company behind it, is Twilio's other non-fixed VoIP example. More in TextNow and verification codes.
Can a non-VoIP number still be rejected?
Yes. Line type is one check among several. A service can also look at your identity, your country or your account's history.
Is a Cleat line non-VoIP?
Yes: a real US mobile line, not VoIP and not a virtual number. It receives texts, and transcripts of incoming calls. It can't place calls or send texts today.
Sources
Facts about other companies come from their own pages, checked in September 2026.
- Twilio, Lookup Line Type Intelligence https://www.twilio.com/docs/lookup/v2-api/line-type-intelligence
- Twilio, filtering VoIP numbers before sending codes https://www.twilio.com/en-us/blog/filter-voip-before-otp-verification
- FTC Data Spotlight, text scams in 2022 https://www.ftc.gov/news-events/data-visualizations/data-spotlight/2023/06/iykyk-top-text-scams-2022
- NIST SP 800-63B, revision 4 https://pages.nist.gov/800-63-4/sp800-63b.html
- NIST SP 800-63B, revision 3 https://pages.nist.gov/800-63-3/sp800-63b.html
- Hushed Help Center https://support.hushed.com/hc/en-us/articles/360015707631
- MySudo Support https://support.mysudo.com/hc/en-us/articles/360019981814
- Quo pricing https://www.quo.com/pricing
- MultiMFA, shared SMS verification number https://multimfa.com/shared-sms-verification-number
- Tello Help Center, activating an eSIM outside the US https://tello.com/help_center/how-to-activate-an-esim-outside-the-us