A2P SMS

A2P SMS (application-to-person SMS) is text messaging sent by a software application on behalf of a business or organisation to a person's phone. One-time passcodes, delivery updates, appointment reminders, fraud alerts and opted-in marketing are all A2P traffic. The opposite is P2P (person-to-person) messaging, which people type to each other.

#How does A2P messaging work?

A business rarely connects to mobile networks directly. Its application calls an SMS API, and the messaging provider passes the message through one or more aggregators to the network that serves the recipient. Each hop takes a fee. The terminating network charges for delivering the message to its subscriber.

Senders identify themselves with one of three kinds of sender IDs, depending on the country:

• Long codes: ordinary phone numbers. In the US, business texting from 10-digit numbers is called 10DLC and needs registration.
• Short codes: 5- or 6-digit numbers leased for high-volume programmes.
• Alphanumeric sender IDs: a brand name instead of a number, allowed in many countries but generally not in the US or Canada.

When the message reaches the handset, or fails, the network can return a delivery receipt.

#How is A2P messaging regulated?

Rules come from law, regulators and the operators themselves. In the US, the wireless industry association CTIA publishes Messaging Principles and Best Practices (May 2023). It calls business traffic "Non-Consumer" messaging and expects senders to get clear consent, honour opt-outs and register how they use their numbers. Many other countries require sender ID registration or ban unregistered alphanumeric senders.

Operators enforce these rules with filters. Traffic that looks unsolicited or arrives over unapproved "grey" routes may be blocked without notice.

#What goes wrong with A2P SMS?

• Invalid and disconnected numbers. Every message to a dead number still costs money and hurts sender reputation.
• Landlines and non-mobile numbers. Most landlines can't receive SMS. See line type.
• Artificially inflated traffic. Bots trigger OTP messages to numbers that earn the attacker a fee. See SMS pumping and IRSF.
• Unclear delivery status. Receipts vary by route, and some routes report less than others.

#Is SMS still the right channel?

Often, because every mobile phone can receive it. But rich channels are growing. RCS adds branded, verified business messaging inside the phone's default app, and many users prefer messengers they already use. Choosing per recipient, with their consent, can lower costs. See choosing a messaging channel by country.

#How does MobileValidate help A2P senders?

MobileValidate checks numbers before you pay for a send. The carrier lookup returns the line type and current carrier, so you can drop landlines and premium-rate numbers and estimate per-network costs. The RCS check shows which opted-in recipients can receive RCS. Inconclusive answers are free. MobileValidate is built for messages people asked for. It must not be used to find targets for unsolicited bulk messaging. See SMS cost reduction for a worked workflow.