Glossary

Short code

A short code is an abbreviated phone number, usually 5 or 6 digits in the US and similar lengths elsewhere, that businesses use to send and receive high-volume application-to-person text messages such as verification codes, alerts and opt-in campaigns.

Updated 26 Sept 2026By PhoneBorn TeamEditorial policy

How short codes work

Short codes are national: a code works only within the country that issued it, and the same digits can belong to different senders in different countries. In the US, common short codes are leased through a registry administered for the wireless industry (associated with CTIA); applicants describe their use case, and carriers must approve it before messages flow. Other countries run their own systems, often through operators or aggregators.

Because each campaign is pre-approved, carriers allow short codes much higher throughput than regular long numbers. This makes them a standard channel for A2P SMS — including large volumes of verification codes.

Why it matters for verification

Many large platforms send OTPs from short codes in some countries and from long numbers or sender IDs in others. For the receiving line, this has a practical consequence: short-code messages are routed by mobile carriers, and some VoIP or internet-based numbers cannot receive them at all. If a code never arrives on such a line, the short code may be the reason.

Short codes also support keyword replies. Texting STOP usually opts you out of a program, and HELP returns contact information — but replying STOP to a verification sender may block future codes from it until you opt back in (often with START).

Examples

A bank texting "Your code is 482913" from a five-digit number.
A retailer's text-to-join campaign ("Text JOIN to 12345").
Two-way alerts, such as confirming an appointment by replying Y.

Short codes generally cannot receive voice calls, and they only work within the country that issued them. For receiving verification texts on a real mobile line, see SMS verification and why codes never arrive.

Put it into practice

Short code: FAQ

Can I receive short-code texts on any phone number?

Mobile numbers on major carriers generally can, within the same country. Many VoIP and internet-based numbers cannot, and short codes do not work across borders, so international senders typically use long numbers or sender IDs instead.

What happens if I reply STOP to a short code?

You are usually unsubscribed from that sender's program, and you may stop receiving its verification codes as well. Replying START or UNSTOP often reverses it, depending on the program.