Glossary

A2P SMS (application-to-person)

A2P SMS (application-to-person SMS) is text messaging sent automatically by a software application or business system to individual people, such as verification codes, alerts, reminders and notifications.

Updated 26 Sept 2026By PhoneBorn TeamEditorial policy

How A2P SMS works

An application calls a messaging provider's API, which passes the message to carriers through aggregators and SMS gateways. The message reaches your phone from a sender that can take several forms:

Short codes: 5–6 digit numbers used for high-volume traffic.
Long codes: ordinary-length numbers enabled for business messaging.
Toll-free numbers, in markets that support texting from them.
Alphanumeric sender IDs: a brand name instead of a number, supported in many countries but not all.

Carriers treat A2P traffic as a distinct category with its own pricing, filtering and registration rules.

Registration and filtering

Because A2P traffic can be abused for spam and phishing, carriers and regulators require senders to identify themselves. In the United States, for example, businesses sending A2P messages over standard local long codes generally register a brand and campaign under the 10DLC framework, and toll-free numbers go through their own verification. Other countries use sender-ID registration or approved-template schemes.

Unregistered or suspicious traffic may be throttled or blocked. Rules differ by country and change regularly, so senders should check their provider's current guidance.

Why it matters for phone verification

Almost every OTP you receive is A2P SMS. When a code fails to arrive, the cause is often somewhere in this chain: the sender's registration, carrier filtering, rate limiting, or the destination network refusing a sender ID. The receiving number matters too, since services choose which numbers they send to.

Receiving A2P messages is ordinary use of a phone number. Sending A2P-style bulk or marketing traffic from a personal line is different: it breaks most carriers' rules, and PhoneBorn's acceptable use policy prohibits bulk and marketing messaging. Developers who need to receive codes programmatically can use the OTP verification API.

Put it into practice

A2P SMS: FAQ

Is an OTP message A2P or P2P?

A2P. Verification codes are generated and sent automatically by an application, so carriers classify them as application-to-person traffic.

What is 10DLC?

10DLC is the US framework for business text messaging over standard 10-digit local numbers. Senders register their brand and use case so carriers can apply appropriate throughput and filtering.

Why do some A2P messages show a brand name instead of a number?

Many countries allow alphanumeric sender IDs, so a business can display its name as the sender. You cannot reply to these messages, and some countries, such as the United States, do not support them for SMS.