How Virtual Numbers Work for SMS Verification

Most services verify a new account by sending a one-time code over SMS. If you are testing a signup flow, running QA across countries, or registering for a service that is not available where you live, you need a phone number that can receive that code. That is what a virtual number is for.

The path a code takes

A virtual number is a real mobile number, held by a carrier, that routes incoming SMS to an API instead of a handset. When you rent one, four things happen in order:

1. Reservation. You pick a country and a service. The provider reserves a number from its pool for a limited window — typically 20 minutes.
2. Use. You type that number into the signup form of the service you are registering for.
3. Delivery. The service sends its SMS. The carrier routes it to the provider, which exposes it through the API.
4. Release. You either finish the order once the code arrives, or cancel it if nothing does. The number returns to the pool.

The window matters. A number is not yours forever — it is yours for the length of that window, and only for the service you selected.

Why numbers are tied to a service

It looks arbitrary at first: why does the API ask which service the number is for?

Because delivery is not uniform. Large platforms maintain lists of number ranges they refuse to send codes to, and those lists differ per platform. A number range that works for one service may be silently dropped by another. Providers track which ranges still deliver for which service, and that pairing is what you are actually renting.

This is also why a number that worked last week can stop working: the range got flagged in the meantime.

When no code arrives

It is a normal outcome, not an exception. The usual causes:

• The service refused the number range.
• The service rate-limited the destination after too many signups.
• The SMS was delayed past the reservation window.

A sound provider treats this as a non-event for your balance: no code delivered means no service rendered, so the amount is returned. On AltiviaCloud, cancelling an order that received no SMS refunds it in full, and an order that expires without a code is refunded automatically — you do not have to ask.

Once a code does arrive, the number counts as delivered. That is the point where the charge sticks.

Choosing a country

Two rules cover most cases:

• Match the audience. If you are testing what a Brazilian user experiences, verify with a Brazilian number. Some services change the flow — or the language of the message — based on the country code.
• Prefer availability over price. A cheap number in a country with a thin pool means retries, and retries cost more time than the price difference is worth.