Guide
Why do apps block VoIP numbers?
You type a number into a sign-up form, press Send code, and the app answers 'this phone number cannot be used for verification'. Nothing was sent. What happened is that the app asked a phone-intelligence service what kind of line that number is, got back 'VoIP', and decided not to risk an SMS. This guide explains how those lookups work, why apps rely on them, which apps are strict, and what you can do, including what we can and cannot promise about our own numbers.
By TempSMSVerifyPublished
Quick answer
Why do apps block VoIP numbers?
Apps run a line-type lookup on every number before sending a code. Services such as Twilio Lookup and Telesign Phone ID label a number as mobile, landline, fixed VoIP or non-fixed VoIP. Because internet numbers are cheap to obtain in bulk, apps treat them as a fraud signal and refuse them to limit fake accounts and SMS pumping.
What happens in the second before the code is sent?
Most sign-up forms do not talk to a carrier directly. They send the number to a phone-intelligence API and wait for a verdict. Twilio Lookup v2, for example, has a Line Type Intelligence package that returns one of a fixed set of labels. Twilio's documentation (checked October 2026) defines 'nonFixedVoip' as 'a virtual phone number obtained online without requiring a physical device. For example, Google Voice or Enflick', and 'fixedVoip' as 'a virtual phone number associated with a physical device. For example, Comcast or Vonage'.
Telesign's Phone ID does the same job with numeric codes. Its phone type table (Telesign developer docs, October 2026) lists 1 fixed line, 2 mobile, 3 prepaid, 4 toll-free, 5 VoIP, 6 pager, 7 payphone, 8 invalid, 9 restricted premium, 10 personal, 11 voicemail and 20 other. Telesign also sells Intelligence, which returns 'a risk recommendation telling you how risky the current transaction is', and the docs say customers use it 'to decide whether to allow, flag, block a phone number'.
The app's developer then writes a rule. A relaxed rule sends the SMS to anything that can receive it. A strict rule allows only 'mobile'. In between sit the apps that allow fixed VoIP but not non-fixed VoIP, or that allow VoIP but ask for extra checks. That rule, not the number itself, is what you run into.
| Label | Twilio Lookup meaning | Telesign code | Typical app rule |
|---|---|---|---|
| Mobile | A mobile number that generally can receive SMS | 2 (mobile), 3 (prepaid) | Allowed almost everywhere |
| Landline | Generally cannot receive SMS | 1 (fixed line) | Allowed only where a voice-call option exists |
| Fixed VoIP | Virtual number tied to a physical device (Comcast, Vonage) | 1 or 5, depending on the carrier record | Allowed by many apps, refused by strict ones |
| Non-fixed VoIP | Virtual number obtained online, no device (Google Voice, Enflick) | 5 (VoIP) | Refused by strict apps |
| Toll-free, premium, pager, voicemail | Special-purpose numbers | 4, 6, 9, 11 | Almost always refused |
| Unknown | Valid number, line type unknown | 20 (other) for many non-US numbers | Depends on the app; often treated as risky |
Why do apps treat VoIP as a risk signal?
Three reasons, and they are about money and abuse, not about you. First, fake accounts. A carrier mobile line usually costs a SIM, a plan and, in many countries, an ID check; an internet number can be created in seconds. Anyone building bots, fake reviews or spam networks needs numbers in volume, so VoIP ranges are where that traffic concentrates, and apps score the whole range accordingly.
Second, SMS pumping. Twilio's own guidance on preventing toll fraud describes attacks where 'fraudsters take advantage of a phone number input field to receive a one-time passcode' at scale, aimed at number ranges where 'the fraudsters get a share of the generated revenue'. Twilio's recommended defenses include rate limits, bot detection, geographic restrictions and carrier lookups so that apps 'only send SMS to mobile numbers'. When an app follows that advice, VoIP numbers stop receiving codes.
Third, account security. NIST Special Publication 800-63B-4 (August 2025) classifies out-of-band authentication over the public telephone network, meaning SMS and voice, as restricted, and tells verifiers to consider risk indicators such as 'device swap, SIM change, number porting, other abnormal behavior'. A number that is easy to obtain and easy to drop is a weak recovery factor, and apps that use the phone for account recovery, such as Steam or Apple, are the strictest for that reason.
Line type is only the first filter. Apps also weigh velocity (codes requested from one device, IP or number), a country mismatch between number and IP, and whether the number already registered other accounts. That is why 'does app X accept VoIP?' never has a permanent answer.
Which apps block VoIP numbers?
Our /sms-verification-requirements index tracks the published phone rules of every app we cover, with a source and a confidence level per row. Apps whose help centers state outright that VoIP or virtual numbers are not accepted include Discord, Steam, Microsoft, Ticketmaster, Blizzard, Craigslist, LINE and Plenty of Fish, which names TextNow and Google Voice. OpenAI refuses VoIP and also caps each number at a small number of verifications. A larger group, including WhatsApp, Telegram, Google, Instagram and TikTok, publishes no blanket ban but refuses some numbers by carrier, country and history.
In that group the decision is per number and per attempt, so an app can accept a number in one country and refuse one in another. And the refusal is often silent: the app says it sent a code, but nothing was ever handed to a carrier.
| App | Published policy | Where it bites |
|---|---|---|
| Discord | Help center: VoIP and temporary numbers not accepted | Phone verification on join; one number per account |
| Steam | Support: VoIP numbers not accepted | Steam Guard and account recovery |
| Microsoft | Support: VoIP not accepted for security info | Adding a phone as security info |
| Ticketmaster | VoIP and Google Voice numbers not accepted | Account verification; presale codes |
| OpenAI (ChatGPT) | Rejects VoIP; up to 3 verifications per number | Sign-up and API platform |
| Craigslist | International and VoIP numbers not accepted | Posting; one code request every 5 minutes |
| WhatsApp, Telegram, Google | No blanket ban; some numbers refused | Varies by country and number history |
What can you do when a number is refused?
Start by reading the error. 'This phone number cannot be used for verification' or 'invalid number' usually means the lookup refused it; no SMS will come, and retrying only burns your attempt quota. 'Too many requests' or 'try again later' means a rate limit, and the fix is to wait, in some apps up to 24 hours. A spinner with no error usually means the code was sent and is delayed; our guide on /blog/verification-code-not-received covers that case.
- Choose SMS rather than a voice call where both are offered; receive-only numbers cannot answer calls.
- Try a different country. Lookup verdicts vary by range, and a country with a different carrier mix often passes where the first one failed.
- Do not loop through many numbers in minutes. Apps count attempts per device and IP as well as per number, and you can lock yourself out.
- For apps that use the phone as a recovery factor, such as Steam, Apple or your main Google account, use a number you will keep, then move 2FA to an authenticator app and save backup codes; see /blog/2fa-backup-codes.
How do TempSMSVerify numbers fit in?
Honestly: we do not know how a given app's lookup will classify a given number, and we will not tell you that our numbers are 'non-VoIP' or pass every check. Our lines come from two providers, HeroSMS and 5sim, across 140+ countries; the catalog shows live stock and price per app and country, and acceptance differs by app, country and the number's history. Some apps we list accept most of our numbers most of the time; the strict apps in the table above refuse many.
What we can promise is the billing rule. Buying a number freezes its price in your balance and reserves the number for up to 20 minutes. You are charged only when an SMS arrives in your dashboard. If the app refuses the number or the code never comes, cancel after about 2 minutes, or mark the number as already used, or simply let it expire: the frozen amount returns to your balance automatically. A refused number costs you time, not money. The flow is described step by step on /how-it-works.
FAQ
FAQ
How does an app know my number is VoIP?
It queries a phone-intelligence API such as Twilio Lookup or Telesign Phone ID, which checks carrier records and returns a line type: mobile, landline, fixed VoIP, non-fixed VoIP and a few special categories. The lookup takes a fraction of a second and happens before any SMS is sent, which is why a refused number never receives anything.
Is it illegal to use a VoIP number for verification?
No. Using an internet-based number is lawful; what matters is what you do with the account. Apps may set their own rules in their terms, and breaking those rules can cost you the account, not a fine. Fraud, impersonation and spam are illegal whatever number you use. Our /blog/is-it-legal-to-use-a-temporary-phone-number guide covers the details.
Will a TempSMSVerify number pass a VoIP check?
Sometimes, and we cannot tell you in advance for a specific app and number. Our lines come from HeroSMS and 5sim and are classified by whatever carrier record the app's lookup sees. We publish each app's stated policy on /sms-verification-requirements. If a number is refused and no SMS arrives, you are not charged.
Why does Discord say my number is invalid?
Discord's help center states that VoIP and temporary numbers are not accepted, and it enforces one phone number per account. 'Invalid phone number' usually means the lookup returned a VoIP type or a number already linked to another account. A carrier mobile line you control is the dependable option for Discord.
Does the same number get blocked everywhere?
No. Each app sets its own rule and each lookup vendor keeps its own carrier records, so one number can be accepted by Telegram and refused by Steam. Country matters too: a range flagged in one country may be fine in another. That is why switching country is the most useful first step after a refusal.
Can I get around a VoIP block?
You can choose a different kind of number, such as a carrier mobile line, a second SIM or an eSIM, which lookups label as mobile. What you should not do is cycle through numbers to force an account onto an app that has refused you, or to come back after a ban; that breaks the app's terms and our /acceptable-use policy.