Glossary

A phone line activated without submitting any identity document, legal name, address or payment card.

KYC — know your customer — is the identity verification regulated providers must perform. A no-KYC number is one sold outside that regime, typically by a reseller leasing carrier ranges and settling in cryptocurrency. It is a real, dialable number; the absence is of paperwork, not of function.

See alsoKYCDID numberVirtual phone number

Know Your Customer: a regulatory duty to verify identity before a service is provided.

Banks, payment institutions and, in many jurisdictions, mobile network operators issuing SIM cards must apply KYC. Number resale occupies a legal space where this requirement does not universally apply. Control of a line, not identity, is what passing an SMS check proves; a phone number is never itself KYC.

See alsoNo-KYC phone number

A real, dialable number. Its calls and messages terminate to software instead of to a SIM card in a handset.

The number exists in the national numbering plan like any other. What differs is the last hop: instead of routing to a mobile switching centre and a SIM, it routes to a gateway that hands the message to a web panel or an API. Senders cannot tell the difference from the routing alone.

See alsoDID numberVoIP vs non-VoIP number

A Direct Inward Dialing number reaches a specific endpoint directly, without a switchboard; each one is individually routable.

What retail calls a virtual number, wholesale calls a DID. Carriers allocate DID blocks to providers, who resell individual numbers. These are the ranges a provider means when it says "we hold ranges".

See alsoVirtual phone numberNational numbering plan

A classification based on which block a number was allocated from, either a VoIP block or a mobile carrier range; the delivery technology does not matter.

Range databases are queried by services, and this single distinction determines most verification outcomes. Mobile-range numbers are treated as people; VoIP-block numbers as disposable. Although both may be delivered over IP, the allocation, not the transport, defines the classification. A provider that will not tell you which block you are buying is almost certainly selling the second.

See alsoNational numbering planRange database

The published allocation of every number range in a country, defining which prefixes are mobile, geographic, toll-free or premium.

Maintained by each country's regulator and published openly. It is why a number starting +33 6 is recognisably a French mobile and +33 1 is a Paris landline. Verification systems check submitted numbers against these plans, which is why the numbering data on our country pages is worth reading before you buy.

See alsoE.164VoIP vs non-VoIP number

The ITU standard for international phone number format: a plus sign, a country code, and the national number, up to fifteen digits total.

Written +33612345678, never 0612345678. The domestic trunk prefix — the leading 0 in most of Europe, 1 in North America, 8 in Russia and Kazakhstan — is dropped in E.164. Entering a number with the trunk prefix intact is the single most common reason a verification code never arrives.

See alsoNational numbering plan

A one-time password is a short numeric code, valid for a few minutes, sent to prove control of a phone number or email address.

Typically four to seven digits. The code proves you can receive messages at that number at that moment — nothing more. It is not identity verification, which is why SMS OTP is considered a weak second factor by security professionals and a strong one by product managers.

See alsoA2P messagingSIM swap

A2P (application-to-person) SMS is automated messaging from a system to a person, different from person-to-person texts.

Every verification code counts as A2P. Carriers route, price, and filter it separately from ordinary texts, and several countries require senders to register A2P traffic. When a valid number receives no code, the usual cause is A2P filtering between the aggregator and the destination.

See alsoOTPSender ID

The alphanumeric or numeric string shown as the origin of an SMS, such as a brand name instead of a number.

Some countries permit arbitrary alphanumeric sender IDs; others require pre-registration or forbid them. This is why the same service appears as a brand name in one country and a random short number in another.

See alsoA2P messaging

A commercial dataset mapping number ranges to carriers, line types and risk scores, queried by services deciding whether to accept a number.

Published numbering plans form the basis, then portability data and observed behaviour are layered on top. When a service says "this number is not supported", it queried such a database and received an unfavourable answer. Providers cannot change that result; they can only offer ranges that score well in those databases.

See alsoVoIP vs non-VoIP numberRecycled number

A recycled number is one previously held by someone else and reissued, potentially carrying that holder's existing service registrations.

Recycling is normal across the whole telecoms industry — carriers reissue disconnected numbers within months. The practical consequence is "this number is already registered" errors on services the previous holder used. Never-recycled pools exist to avoid this and cost more because each number can only be sold once.

See alsoNever-recycled pool

A set of numbers that have never been allocated to any prior holder and have no registration history on any service.

Required for services that check registration history aggressively — Google above all, and Apple to a lesser extent. The premium reflects genuine scarcity: a never-recycled number can be sold exactly once and stops being one the moment it is used.

See alsoRecycled number

An eSIM is an embedded SIM profile downloaded over the air to a device, replacing the need for a physical card.

With an eSIM you still hold a SIM: mobile data plus a number, issued under whatever conditions the seller required. Anonymity is not built in, eSIM-capable hardware is needed, and a free profile slot must be available. A virtual number asks for only a browser.

See alsoVirtual phone number

A SIM-swap attack is when someone persuades a mobile carrier to port a victim's number onto a SIM the attacker controls.

The dominant real-world attack against SMS two-factor authentication, and the reason security people dislike SMS OTP. It is a social-engineering attack on carrier support staff, which is why it works against numbers backed by large call centres and rather less well against numbers with no account and no support line to socially engineer.

See alsoOTP

The regulatory right to keep a phone number when changing provider.

Portability is why range databases are imperfect: a number allocated to one carrier may now be served by another. It also means the range a number was issued from does not always describe who serves it today, which is a source of inconsistent verification results across services.

See alsoRange database

Underpaid coverage is a tolerance band in a crypto invoice inside which a slightly-short payment still settles the order.

Wallets often deduct the network fee from the typed amount instead of adding it, so the merchant receives marginally less than invoiced. The invoice fails without coverage, leaving funds in limbo. A two to three percent coverage setting absorbs essentially every wallet fee quirk.

See alsoInvoice lifetime

An invoice lifetime is the window during which a crypto invoice holds its quoted exchange rate and remains payable.

The window is finite because the merchant absorbs the price risk. Paying after expiry routes funds to a dead invoice, which then needs manual reconciliation. At ninety minutes, ours comfortably outlasts a Bitcoin confirmation at normal fee levels.

See alsoUnderpaid coverage