What is A2P SMS?
A2P SMS stands for application-to-person messaging. It is any text message sent by a piece of software to a person's mobile phone: a one-time password from a bank, a delivery update from a courier, an appointment reminder from a clinic, a sale announcement from a shop. The sender is a system, the recipient is a human, and the message travels through a messaging platform instead of from one handset to another.
It matters because the mobile industry treats it as a different kind of traffic from texts between friends. Operators meter it, filter it and, in many countries, require businesses to register before they can send it. If you send messages for a living, A2P rules are the reason messages are delivered or silently dropped.
A2P vs P2P: what is the difference?
| P2P (person-to-person) | A2P (application-to-person) | |
|---|---|---|
| Sender | A person using a phone | Software using an API or platform |
| Volume | A few messages at a time | From one to millions |
| Sender identity | Phone number of the person | Registered sender ID, long code, short code or toll-free number |
| Cost to the sender | Often bundled in a mobile plan | Charged per message segment |
| Delivery reporting | Usually none | Delivery receipts, error codes |
| Regulation | Light | Registration, templates, consent, sending hours |
| Spam controls | Standard filtering | Strict, and tied to the sender's registration |
The line is not always obvious. A person using a phone to send fifty messages to customers is acting commercially, and operators may block or throttle that number. The other direction is worse: some low-cost providers disguise A2P traffic as P2P through consumer SIM cards, which is how grey routes work. They are cheap until an operator detects them, which is typically in the middle of a campaign.
How A2P SMS is delivered
Your application calls an API or opens an SMPP connection to a messaging platform. The platform checks registration and content, chooses a route to the operator, and the operator delivers the message to the handset and reports back. Our SMS gateway guide describes each stage, and the SMPP documentation covers the protocol for high volume.
Types of route
| Route | What it is | Trade-off |
|---|---|---|
| Direct operator | The platform connects to the operator's SMS centre | Best delivery and speed; the highest cost |
| Aggregator | The platform buys from a partner with direct links | Good quality at lower cost; one extra hop |
| Grey route | A2P disguised as P2P or routed through unauthorised paths | Cheap, unreliable, may be blocked without notice |
What an A2P API call carries
Registration details travel with each message or are stored against your sender in the platform. This sketch shows the idea for an India transactional message; fields are illustrative, and the real names are in the API reference.
{
"channel": "sms",
"to": "+919812345670",
"sender": "TELNXO",
"category": "transactional",
"template": "order_update",
"variables": { "name": "Asha", "order": "4821" },
"callback_url": "https://example.com/hooks/sms"
}A2P rules in the markets we serve
Every country draws the line in a slightly different place, but the principle is the same: identify yourself, tell the network what you will send, and respect the recipient. Here are the main regimes at a glance.
| Market | What is required | Where to start |
|---|---|---|
| India | DLT registration of your entity, sender ID (header) and each message template. Promotional messages follow DND and time-of-day rules. | DLT checklist and bulk SMS guide |
| United States | 10DLC brand and campaign registration for local numbers, or toll-free verification, or a short code. Alphanumeric sender IDs are generally not supported. | Register with The Campaign Registry through your provider |
| United Kingdom | Alphanumeric sender IDs are supported without a national registry, but operators filter spam, and consent rules apply to marketing. | Follow Ofcom guidance and use a recognisable sender ID |
| UAE and Gulf | Sender ID registration with the operators, often with a local trade licence, plus content rules. | Check sender ID rules by country |
| Singapore | Alphanumeric sender IDs must be registered through the national SMS Sender ID Registry. | Register via SSIR |
Rules change. Registration requirements and fees are updated by regulators and operators several times a year. Treat the table as a map, not a legal opinion, and confirm the current rules with your provider before you launch in a new country.
Types of A2P message
- OTP and authentication. Highest priority, shortest lifetime. See what is an OTP SMS.
- Transactional. Confirmations and receipts triggered by something the customer did. See our transactional solution.
- Service and reminders. Appointment notices, bill due dates, delivery updates.
- Promotional. Offers and marketing. Strictest rules, including consent and time windows. See marketing.
- Two-way conversational. Customers reply, and a person or bot answers. Needs a number that can receive messages.
How to choose an A2P SMS provider
- Ask about routes. Direct or aggregator, and for which countries. Anything described only as "cheap" deserves questions.
- Check registration support. Will they help with DLT, 10DLC, toll-free verification or sender ID registration, and do they do it for you?
- Test delivery. Send a pilot to your real audience, on several operators, and read the receipts.
- Look at reporting. Per-message status, error codes with meaning, and webhooks you can use.
- Compare all-in cost. Include registration, number rental and minimum commitments, not only price per message. The pricing page and cost calculator show how to model it.
If you are moving from another platform, our guides for Twilio, Infobip and Sinch show how senders, numbers and webhooks map across.
What A2P SMS costs
You pay per message segment, and four things set the rate: the destination country, the route type, the message category and your monthly volume. Registration adds one-off or recurring charges in some markets: a DLT registration fee in India, brand and campaign fees for 10DLC in the United States, and monthly rental for numbers. A provider that quotes one flat price for the whole world is usually hiding a route compromise.
Encoding changes the total more than most people expect. A message with one emoji or a Hindi or Arabic character is sent as Unicode, so it holds 70 characters instead of 160 and splits sooner. The guide to segments, encoding and cost shows the arithmetic, and the Unicode checker flags the characters that cause it.
A2P SMS in practice: three examples
| Business | Message | What it needs |
|---|---|---|
| Bank | OTP and payment alerts to customers in India and the Gulf | Registered headers and templates, a fast direct route, delivery receipts for audit |
| Online store | Order, dispatch and delivery updates to buyers in the UK and US | A registered 10DLC campaign or toll-free number, links on a stable domain, opt-out handling |
| Clinic group | Appointment reminders in Singapore and the UAE | A registered sender ID in each country, quiet hours, no sensitive details in the text |
In each case the technical part is a short API call. The work is in getting the identity, the content and the consent right before the first message goes out, and in watching delivery afterwards so problems surface in hours rather than weeks.
Best practices for A2P SMS
- Get consent and keep a record: who, when, where and what they saw.
- Identify the brand in the first few words so the message is recognisable.
- Offer a clear opt-out on promotional messages and honour it immediately.
- Keep to one segment where you can. Check drafts with the segment calculator.
- Avoid public URL shorteners that operators flag; use your own short domain.
- Respect local sending hours and do not send promotions at night.
- Use separate sender IDs or numbers for OTP and for marketing, so a complaint on one does not hurt the other.
Beyond SMS
SMS is the base layer, not the whole story. Customers on WhatsApp expect WhatsApp messages, and Android users can receive branded cards through RCS. Many businesses now send over the best available channel and fall back to SMS. You can do that from one API with Telnxo SMS and our other channels.
A2P is not a technical detail. It decides whether your message reaches the person at all.
Send A2P SMS on compliant routes. We help with registration, route choice and delivery monitoring in every market we cover.
Frequently asked questions
What does A2P mean in SMS?
A2P stands for application-to-person. It describes text messages sent from software, such as a banking app, an online store or a CRM, to a person's mobile phone.
What is the difference between A2P and P2P SMS?
P2P is a message from one person's phone to another person's phone. A2P is sent by an application through a messaging platform. Operators price, monitor and regulate A2P separately because it is commercial traffic at scale.
Is A2P SMS regulated?
Yes, in most countries. India requires DLT registration of entities, headers and templates. The US requires 10DLC brand and campaign registration or toll-free verification. The Gulf states and Singapore have sender ID registries.
What is A2P 10DLC?
10DLC stands for 10-digit long code. It is the US system that lets businesses send A2P messages from standard local numbers after registering their brand and campaign with the carriers through The Campaign Registry.
Why are A2P messages blocked?
Common reasons are missing registration, content that matches spam patterns, unregistered links, sending to numbers that opted out and traffic that arrives over routes operators treat as grey or unauthorised.
Is A2P SMS more expensive than P2P?
Per message, yes, because operators charge termination fees for A2P traffic and providers pay for registration and route quality. The cost is justified by delivery assurance, receipts and compliance.
Can I send A2P SMS from my own phone?
You can send a few messages, but it is not A2P in the regulated sense and breaks most operator terms when used for business at volume. For commercial messaging, use a platform that sends through authorised A2P routes.