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SMS by API

Send SMS by API,
from your own number.

Install the free Android app, sign in, and every SMS you send through the Unlimited Messaging API leaves from your phone's SIM card, on your own carrier plan. Recipients see your number, replies come back to your inbox and webhooks, and the same request can also go out on WhatsApp and email.

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The context

What does sending SMS by API from your phone mean?

Sending SMS by API from your own number means your code calls a REST endpoint, and the text leaves as a normal SMS from a phone you own. With Unlimited Messaging, that phone runs our free, open source Android app.

Classic SMS APIs work differently. You rent a sender number or a short code from a provider, the message travels over the A2P (application-to-person) network, and each segment of 160 characters is billed, at a rate that changes from one country to the next. In the United States you also register a brand and a campaign (A2P 10DLC) before sending.

With the Android app, the phone keeps one connection open to the Unlimited Messaging API. When you call POST /message with "channel": "SMS", the API hands the message to the phone, the phone sends it from its SIM, and each status comes back as the network confirms it: queued, sending, sent, delivered when your carrier returns delivery reports, undeliverable or failed. SMS has no read receipts, so there is no "read" status.

The SMS goes on your own plan, so Unlimited Messaging adds no per-message fee, and recipients see the number they already know. SMS received after you sign in come back to your inbox and the message.received webhook. It suits your own traffic at a human pace: reminders, codes, follow-ups, an AI agent texting your customers. Bulk campaigns still belong to a dedicated SMS provider.

Illustration: a phone with text-message bubbles and an SMS tag, with the headline “SMS caps you at 160 characters”.

The request

One curl to send an SMS, one more line to add WhatsApp and email

The SMS channel uses the same POST /message endpoint as WhatsApp and email. Name it in channels, give a phone number, and it leaves from your phone. Add up to three channels to reach the same person everywhere in one request.

curlShell
curl https://api.unlimitedmessaging.app/message \
  -H "Authorization: Bearer $UM_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "to": {
    "phone": "+33612345678"
  },
  "channels": [
    {
      "channel": "SMS"
    }
  ],
  "text": "Your appointment is tomorrow at 10:00."
}'
An SMS from your own SIM. With dual SIM, add "accountId" to the channel entry to pick the line.
POST /messageJSON
{
  "to": {
    "phone": "+33612345678",
    "email": "[email protected]"
  },
  "subject": "Your appointment tomorrow at 10:00",
  "text": "Hello, this is a reminder that your appointment is tomorrow at 10:00. Reply to this message if you need to move it.",
  "channels": [
    {
      "channel": "WHATSAPP"
    },
    {
      "channel": "SMS",
      "text": "Your appointment is tomorrow at 10:00."
    },
    {
      "channel": "EMAIL"
    }
  ]
}
One request, three messages: each channel gets its own copy, sharing one dispatchId. The SMS entry overrides the text with a shorter version.

Comparison

Classic SMS API vs SMS from your own phone

Both send an SMS from your code. They do not suit the same jobs: here is where each one is the better choice, honestly.

Classic SMS API vs SMS from your own phone
Classic SMS APITwilio-style, A2PUnlimited Messagingyour Android phone
SenderA number or short code rented from the providerYour own number, the one your customers know
Cost per SMSBilled per 160-character segment, varies by countryYour carrier plan, no per-SMS fee added by us
SetupBuy a number, register sender (A2P 10DLC in the US)Install the app, sign in, your SIM appears
VolumeHigh throughput, built for campaignsHuman pace, about 30 SMS per window before Android asks
InfrastructureNothing to keep running on your sideA phone that stays on, charged and connected
RepliesWebhook to your serverSame inbox and webhook as WhatsApp and email
Other channelsSMS only, or separate productsWhatsApp, email and SMS in one request
Delivery statusCarrier delivery receiptsSent, and delivered when your carrier reports it

Our approach

SMS as one more channel of the same API

We did not build an SMS provider. We made your phone a channel of the API you already use for WhatsApp and email, with the same statuses, webhooks, SDKs and MCP server.

Your SIM, your number, your plan

The SMS leaves from the phone in your pocket or on a desk at the office. Recipients see your usual number, and the cost is whatever your carrier plan already charges.

  1. Two-way

    SMS received after you sign in come back to your inbox and the message.received webhook, next to your WhatsApp and email conversations.

  2. Dual SIM

    Each SIM becomes its own SMS account. Pick the line per message with accountId, or let the API choose.

  3. Open source, no tracking

    The app is MIT licensed, with no Firebase, no Play Services and no analytics. You can read exactly what an app holding SMS permissions does.

Per-SMS fee added by Unlimited Messaging
0Per-SMS fee added by Unlimited Messaging
Channels in one request: WhatsApp, SMS, email
3Channels in one request: WhatsApp, SMS, email
Characters max per SMS, sent in up to 10 parts
1530Characters max per SMS, sent in up to 10 parts
Android version required
8.0+Android version required

How it works

From zero to your first SMS in three steps

  1. 01

    Install the app

    Download the APK on your Android phone from the Android page or GitHub Releases. It is not on Google Play, which reserves SMS permissions to default SMS apps. If Play Protect blocks the install or Android refuses the SMS permission, the FAQ below shows how to unblock it.

  2. 02

    Sign in

    Tap Sign in: the website's own login opens in a browser tab (email, magic link, Google or GitHub). The app never sees your password, and each SIM appears as an SMS account.

  3. 03

    Send

    Call POST /message with "channel": "SMS", or send from the dashboard, the SDKs, n8n or an AI assistant through the MCP server. Statuses and replies arrive by webhook.

FAQ

Questions about sending SMS by API from your phone

Sources

Sources & references

To check the information in this article for yourself:

  1. Unlimited Messaging for Android - source code and releasesGitHub
  2. SmsManager - API referenceAndroid Developers
  3. Use of SMS or Call Log permission groupsGoogle Play Console Help
  4. How long can a message be? SMS segments and character limitsTwilio
  5. SMS pricing - per segment and per countryTwilio
  6. A2P 10DLC - registration for application messaging in the USTwilio
Ilian, senior software engineer

Written by

· Senior Software Engineer

A senior software engineer, he founds and runs several tech companies. He builds products around messaging APIs, automation and AI integration, and shares here what he learns while building.

View LinkedIn profileUpdated

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