A secondary number can keep your personal number off many sign-up forms, but no virtual or prepaid service is guaranteed to receive every verification code. The site you are signing up with decides which number types it accepts, so the practical question is not which service is best in general but which one a specific site will accept. For accounts that matter, treat SMS as a fallback rather than the first choice, because NIST describes phone- and SMS-based codes as a restricted authenticator type. In the United States, Login.gov, for example, excludes Google Voice, similar VoIP numbers, and most prepaid numbers from its phone-verification step.
What a secondary number does and does not do
A secondary number separates the phone number a site stores from the one you give out to everyone. That separation is useful for marketing lists, data-broker exposure, and sign-ups for services you rarely use. It does not change how SMS works, and it does not guarantee that the other side will accept the number.
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- It can keep your primary number off the form when the site only needs a phone number to send a one-time code.
- It does not ensure acceptance. Many sites block or reject VoIP and prepaid numbers, and some check whether the number is the one the account holder actually uses.
- It becomes part of the account. If the site later uses that number for login or recovery, losing access to it can lock you out.
- It does not make SMS stronger. A code sent to a second number travels over the same channel as a code sent to your main number.
Comparing the main options
The options below differ in number type, whether you keep the number long term, and how much each destination site is likely to trust it. Compare them on those factors rather than on a single ranking.
| Option | Where it may fit | Limits and checks |
|---|---|---|
| Google Voice or a similar VoIP number | A secondary contact number for services that accept VoIP numbers | Creating a Google Voice number itself requires a text verification code. Login.gov explicitly does not accept Google Voice or similar VoIP numbers for its phone check. (Google Voice Help; Login.gov) |
| TextNow number, SIM, or paid number-retention subscription | Low-cost codes for senders that support TextNow numbers | TextNow states that some services reject its VoIP numbers, and that most codes can be received after activating a TextNow SIM or buying a listed recurring subscription. It does not guarantee acceptance across senders. Free Wi-Fi numbers can be recycled after inactivity. (TextNow Support) |
| Prepaid cellular SIM or number | A distinct mobile number when a carrier-issued cellular line is appropriate for you | Do not assume “prepaid” means acceptable. Login.gov says it does not accept most prepaid numbers. Check carrier eligibility, coverage, recurring costs, how the carrier handles inactive numbers, and the destination site’s rules. |
| Public disposable SMS gateway | Not recommended for any account you care about | Public inboxes expose received codes to anyone else using the same number. A 2023 paper on disposable phone numbers reports their use in fraudulent account creation or access and in bypassing verification. (arXiv) |
| Authenticator app or another non-SMS method | Accounts where the site offers a stronger option | A code sent to a separate phone number is still SMS authentication. Where a site offers a non-SMS method, it is generally the better choice for security-sensitive accounts. |
Service-by-service notes
Google Voice
Google says it sends a text verification code when you sign up or add a phone to your account, and it tells users not to share those codes. Its help pages also describe how to disconnect an associated number, which matters if you later want to release the number or change recovery details. Google Voice acceptance by third-party sites is a separate question and is not established by these pages.
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Google’s privacy help states that texts and attachments are stored in Google’s data centers, encrypted in transit between a Voice client and Google and at rest, and synced across your devices. That describes the service’s handling of your data. It is not end-to-end encryption, so it does not keep the messages private from Google. (Google Voice privacy help)
TextNow
TextNow’s support article, updated June 23, 2026, says most verification codes can be received after you activate a TextNow SIM or buy one of its listed recurring subscriptions. The same article says some services reject TextNow VoIP numbers, that Canadian verification codes are largely unsupported, and that acceptance is not guaranteed.
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The number-recycling warning deserves attention. TextNow explains that inactive free Wi-Fi numbers can be recycled. If that happens, you can lose access to any account tied to the number, and whoever later receives the number may be able to see codes sent to it.
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Login.gov’s phone-verification rules show how strict a destination site can be. It says the verification number must be US-based. It accepts home, cell or mobile, and landline numbers, and it does not accept international numbers, some US territories, Google Voice or similar VoIP numbers, premium-rate numbers, or most prepaid numbers. It also says it is most likely to verify your primary or most-used number. These are Login.gov’s rules for its own identity flow, not rules that apply to other websites. (Login.gov help)
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Prepaid cellular numbers
A prepaid SIM gives you a number that behaves like a normal mobile line, which is why some sites accept it where they reject VoIP. Acceptance still depends on the destination. Login.gov’s rules show that a prepaid line can fail the same check that a VoIP number fails. Before buying one for account use, confirm that the carrier keeps the number active for as long as you need it.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why public disposable numbers are a poor choice
Public disposable numbers are shared by design. Anyone who uses the same number can see the codes sent to it, so a code for your account may reach a stranger before you do. The 2023 arXiv paper “Your Code is 0000: An Analysis of the Disposable Phone Numbers Ecosystem” studies public disposable-number gateways and reports their use for fraudulent account creation and access and for bypassing verification. Treat any shared public inbox as unsuitable for private, important, or recoverable accounts.
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The security limits of SMS codes
NIST SP 800-63-4 describes PSTN-based authenticators, including phone- and SMS-based one-time passcodes, as restricted, and it expects services to inform subscribers of the risks and of available alternatives. A secondary number can help with contact privacy, but it does not remove the weaknesses of SMS as an authentication channel. For accounts that hold money, personal records, or the recovery path for other accounts, use the stronger non-SMS option the site offers, such as an authenticator app. (NIST SP 800-63-4, Authenticators)
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- Decide whether the account needs a number only for a one-time code or also for login and account recovery. If it is for recovery, use a number you will keep for years.
- Check the site’s help pages for accepted number types. If they are silent, assume VoIP and prepaid numbers may be rejected and plan for a fallback.
- Confirm the number’s retention terms. For TextNow free Wi-Fi numbers, that means watching for inactivity rules. For a carrier line, confirm the plan keeps the number active.
- Look for a non-SMS option in the account’s security settings and enable it where available.
- Store the site’s recovery codes in a password manager or another secure location, so you can recover the account if the secondary number stops working.
- For any account you do not want to lose, avoid public disposable numbers entirely.
Acceptance and availability vary by destination service and by country. Use the steps above to test each site on its own terms, because no single service can be assumed to deliver codes to every site.
Quick Recap
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