Why VoIP Numbers Get Rejected for SMS Verification

What a VoIP Number Is and Why Platforms Care

A VoIP number is one that terminates on an internet service instead of a SIM card in a handset. Google Voice, TextNow, Hushed, Burner, and most app-based second-line services buy their inventory in bulk from wholesale carriers such as Bandwidth, Inteliquent, and Twilio. Those wholesale ranges are registered in the numbering databases as non-fixed VoIP, not as mobile.

Platforms care because VoIP numbers are cheap to obtain in volume, which makes them the default tool for spam registration and account farming. A fraud team that blocks every number typed as VoIP removes a large share of automated signups at the cost of turning away a smaller group of legitimate users. Most of them accept that trade.

The result is that the number type, not the number itself, decides whether the verification SMS is ever sent. A number can be in perfect working order, receive texts from friends, and still be refused by WhatsApp because of how its range is classified.

How Carrier Lookup Identifies Number Type

Before sending a verification code, most large platforms run the number through a lookup API. Twilio Lookup with the line type intelligence package returns a type field with values such as mobile, landline, fixedVoip, nonFixedVoip, and personal, plus the carrier name and mobile network code. TeleSign PhoneID returns a similar phone type classification alongside a risk score built from porting history and prior abuse reports. Vonage Number Insight and Telnyx offer the same data.

The classification comes from the numbering plan authority in each country and the number portability database, cross-referenced with the carrier that currently owns the range. For US numbers this means the NPAC porting database and the OCN assigned to each block. For UK numbers it is the Ofcom numbering allocation plus the porting records held by the network operators.

Some platforms go a step further and check line status, whether the number was recently ported, and how many times the same number has appeared in their own signup logs. A number that passed the type check but has registered fifty accounts in a month gets blocked on velocity instead.

• Type check: mobile, landline, VoIP, or unknown, returned in under a second
• Carrier identity: the network that currently owns the range
• Porting history: recently ported numbers are treated as higher risk
• Internal velocity: how many accounts this number has already verified on the platform
• Country-level rules: some platforms block whole ranges or whole countries for specific products

Why Google Voice, TextNow, and Hushed Fail

Google Voice numbers are provisioned through Bandwidth and come back from lookup as nonFixedVoip with Google listed as the carrier. That combination is on the deny list of nearly every consumer platform that runs a lookup, including WhatsApp, Telegram, Tinder, and Google itself, which refuses Google Voice numbers as a recovery phone for a new Gmail account.

TextNow assigns numbers from its own carrier partnerships and from Bandwidth and Inteliquent ranges. Lookup returns VoIP, and the TextNow name is well known to fraud teams because the app has been the default tool for throwaway accounts for a decade. Hushed and Burner use similar wholesale inventory and get the same classification.

A second problem is reuse. These apps recycle numbers between users every few weeks, so the number you receive today has often been registered on the target platform by someone else already. Even where the type check passes, the duplicate registration check fails.

Platform by Platform: WhatsApp, Telegram, Google, Tinder

WhatsApp is the strictest of the four. It rejects VoIP types outright, blocks many landline ranges, and applies per-country rules that change without notice. The error is usually a generic message that the number cannot be used for WhatsApp, with no indication that a type check failed. See /whatsapp-phone-number for the countries that currently pass.

Telegram accepts a wider set of ranges than WhatsApp but still refuses well-known VoIP carriers and applies a heavy velocity check. Numbers that have registered several Telegram accounts get a message that the number was banned. Details on which countries receive Telegram codes reliably are at /telegram-phone-number.

Google runs its own lookup and rejects VoIP for account creation and for the recovery phone field, though it sometimes allows a VoIP number for 2-Step Verification on an account that already exists. Tinder uses a third-party lookup and blocks VoIP at signup, then layers device and photo checks on top, so a passing number is necessary but not sufficient.

What a Carrier Range Means at TempNumber.me

TempNumber.me numbers come from ranges allocated to real mobile network operators: EE, O2, Vodafone, and Three in the UK, T-Mobile and Telekom in Germany, KPN and Odido in the Netherlands, and equivalents across 198 countries. When a platform runs a lookup on one of these numbers, the type field returns mobile and the carrier field returns the operator name, which is the same result a personal SIM would give.

The other half of the difference is who else has used the number. A public receive-SMS site puts one number in front of thousands of visitors, so by the time you try it the number is already registered on WhatsApp, Telegram, and Google. A private number from TempNumber.me is assigned to one account for the session, so the duplicate registration check is far less likely to trip.

The credit-based model means you pay per verification or per rental rather than a monthly fee, and the price of each number is shown before you confirm. There is no separate charge for the lookup result being right.

When a Carrier Number Still Gets Rejected

A mobile-type number is not a guarantee. Carrier ranges that have been used heavily for verification across the whole industry can end up on a platform-specific deny list, and a lookup returning mobile does nothing to help once WhatsApp has decided to block that block of numbers. This happens most often with the cheapest ranges in high-volume countries.

Platforms also apply country-level rules. Google has periodically refused all numbers from certain countries for new account creation, and WhatsApp tightens rules on individual prefixes during abuse waves. These decisions are made on the platform side and no number provider can override them.

So a rejection is possible even with a correctly typed number. The right response is not to keep retrying the same number, which only adds to its velocity score, but to switch country or move from a shared number to a private one.

What to Do After a Rejection

Treat the first rejection as information rather than a failure. The sequence below resolves the large majority of cases within two or three attempts.

• Confirm the error is about the number and not about the code. A wrong-code error means the SMS arrived and the problem is elsewhere.
• Do not request the code again on the same number more than once. Repeated requests increase the velocity score and can get the number blocked for everyone.
• Switch to a different country. Rejections are often range-specific, and a number from the Netherlands or Poland frequently passes where a US number was refused.
• Move from a shared number to a private number. Private numbers on TempNumber.me have not been exposed to other users on the same platform.
• If the platform is WhatsApp or Telegram, check the country notes at /whatsapp-phone-number and /telegram-phone-number before choosing.
• If nothing arrives after a plausible attempt, contact support@tempnumber.me with the number and platform. Cases are reviewed individually.