Integrating SMS Messaging into a Mobile App

Imagine your backend sending 10,000 SMS synchronously via HTTP. Each request takes 100–500 ms, the server hangs for minutes, Twilio's limit of 1 SMS/sec on a regular number is exceeded in seconds, and half the messages return a 429 error. Budget wasted, users unhappy. We have seen these scenarios dozens of times.

Recently, a project with 500,000 users in Russia and CIS came to us. The client used Twilio, paying $0.08 per message instead of $0.02 from a local provider. After migrating to SMSC and setting up a queue with a 30 msg/s limit, we reduced costs by 60% and eliminated message loss. On another project, we decreased the per-message cost from $0.07 to $0.02, saving the client over $2,000 per month.

The solution is an async queue with throttling and a well-chosen gateway. Below, we break down the architecture that handles load without burning your budget.

Over 7 years, we have integrated SMS messaging into 30+ mobile apps—from startups to enterprise projects with millions of users. Our experience shows that 80% of delivery issues stem from improper rate limiting configuration and choosing a gateway not suited for the target geography.

Which gateway to choose?

Compare popular options:

Typical gateway rate limits:

If your audience is in Russia and CIS—choose SMSC or similar. For international projects—Twilio or Infobip. We help you select the optimal option for your budget and requirements.

const Queue = require('bull');
const smsQueue = new Queue('sms', 'redis://localhost:6379');

smsQueue.process(5, async (job) => {
  const { to, body } = job.data;
  await twilio.messages.create({ to, from, body });
  await delay(1000 / 5); // 5 msg/sec
});

How to avoid rate limiting?

Rate limiting is the main challenge in bulk messaging. Exceeding limits leads to blocking and message loss. The proper architecture: a task queue (e.g., RabbitMQ or Redis + BullMQ) and workers with throttling. Each worker picks up a task, sends the SMS, waits an interval, then proceeds. To speed up, multiple workers run in parallel, controlling overall throughput.

Why not send SMS synchronously?

Attempting to send 10,000 SMS in a single loop of HTTP requests leads to:

• Backend being blocked for the duration of all requests (each takes 100-500 ms).
• Exceeding the gateway's limit—some requests return a 429 error.
• No retry logic for network failures.

A queue solves all three: requests are non-blocking, limits are respected, and failed tasks are automatically retried. Rate limiting is a mechanism to account for at the design stage.

What's included in the integration work?

1. Requirements analysis: audit of the current app, gateway selection, budget estimation.
2. Server side: queue design (RabbitMQ / Redis), worker implementation with throttling, webhook configuration for statuses.
3. Mobile client: message composition form (with character counter), recipient segment selection, progress tracking via WebSocket/SSE.
4. Testing: load testing up to 50,000 messages, rate limiting verification.
5. Documentation: API description, schemas, operation manual.
6. Support: 3-month warranty, consultations.

The result—a reliable messaging system ready for scaling.

How to track delivery statuses?

Twilio sends a webhook to your endpoint on every status change: queued → sending → sent → delivered or undelivered/failed. The backend aggregates these statuses, and the mobile client requests a summary via a REST endpoint:

GET /admin/sms/jobs/{jobId}/stats
→ { "total": 5000, "sent": 4823, "delivered": 4601, "failed": 177 }

If the gateway doesn't support webhooks (like SMSC on low-cost plans), the backend polls for statuses on a schedule.

Common mistakes when integrating SMS messaging

• Ignoring rate limiting—leads to blocking and message loss.
• Choosing a gateway solely on price—a cheap gateway may lack webhook statuses, complicating tracking.
• Synchronous sending—backend hangs and limits are exceeded.
• No retry logic—messages are lost on transient failures.

Timeline and cost

Gateway integration (Twilio or SMSC), queue implementation, mobile UI with character counter, segment selection, and progress tracking—from 5 to 8 business days. Cost is calculated individually based on complexity and chosen gateway. Get a consultation from our engineer—they will select the gateway for your budget and load. Contact us for an assessment of your project—we will offer the best turnkey solution.

Push Notifications in Mobile App: APNs, FCM, Segmentation, Rich Push

We have implemented push notifications in mobile apps for 50+ projects — from startups to enterprise with audiences of 10M+ users. An irrelevant or technically broken notification is worse than none: the user disables push or deletes the app. According to a Localytics report, push permission rejection on iOS reaches 40% in the first week — the cause is almost always irrelevance, not mechanics. Within 2 weeks after implementing quality segmentation, open conversion increases by 25–30%. Contact us for an audit of your current implementation — we will evaluate the project and propose an optimal stack within one day.

How the Infrastructure Works: APNs and FCM

APNs is the only delivery channel on iOS. Everything else (OneSignal, Braze, Airship) is a wrapper on top of it. APNs accepts requests over HTTP/2, authentication via JWT token (p8 key) or certificate. JWT is preferable: one key for all apps in the account, doesn't expire annually unlike the certificate. For more details, see the official documentation.

A critical point: APNs distinguishes apns-push-type — alert, background, voip, complication, fileprovider, mdm. An incorrect type on iOS 13+ causes background notifications not to wake the app. We've seen projects where content-available: 1 was sent without apns-push-type: background — the app didn't receive silent push on some devices, and the team spent a month looking for an 'app bug'.

FCM on Android works through Google Play Services. For devices without GMS (Huawei, part of the Chinese market), Huawei Push Kit or a direct WebSocket is needed — a separate task. FCM supports data messages (handled in onMessageReceived) and notification messages (the system displays automatically if the app is in the background). Mixing them requires caution: if the notification block has a click_action but the deep link is not registered in the app, tapping the notification simply opens the main screen without navigation.

Why Segmentation Is the Foundation of Effective Push Notifications?

Sending to everyone indiscriminately quickly exhausts user loyalty. Personalized messages are clicked 3 times more often than bulk ones, and proper segmentation reduces churn by 25% (on one project it brought significant additional revenue per quarter). The cost of setting up segmentation in OneSignal or a custom backend depends on the complexity of filters.

Proper segmentation is built on several levels.

Topics are for broad categories: 'new promotions', 'order status updates'. User subscribes via FirebaseMessaging.getInstance().subscribeToTopic("orders"). Simple, but no flexible filtering.

Attribute-based segments — via OneSignal, Braze, or custom backend. We store in the user profile: language, device type, last activity, LTV segment. Notification goes only to those with last_active < 7_days and plan = premium. OneSignal allows building such filters in the interface without code.

Personalized — by specific device_token. It's important to store tokens correctly: the token updates on app reinstall, restoration from backup on a new phone, or resetting settings. On iOS, use UNUserNotificationCenter + didRegisterForRemoteNotificationsWithDeviceToken, save to backend on every launch, not just the first. Otherwise, after 3 months 30% of tokens in the database are outdated.

What Is Rich Push and How Does It Boost Conversion?

A standard notification with title and text is clicked less often than a rich push with image and action buttons — by 3 times. But implementing rich push is a separate task on each platform.

On iOS, rich content requires UNNotificationServiceExtension (to modify payload) and UNNotificationContentExtension (custom UI). The extension runs in a separate process with limited time and memory. If the extension crashes or exceeds the timeout, the system shows the original payload without media. A typical mistake is trying to load an image over HTTP (not HTTPS): ATS blocks the request, the extension silently fails, and the user sees a notification without an image.

On Android with API 26+, notifications are tied to NotificationChannel. If the channel is created with IMPORTANCE_LOW, sound and vibration are unavailable. Different notification types (transactional, marketing) should be in different channels so the user can disable marketing without losing order notifications. BigPictureStyle, MessagingStyle, InboxStyle are templates for expanded notifications. MessagingStyle with Person and avatars is the best choice for chats.

How to Track Delivery and Conversion of Push Notifications?

Sending a notification is half the work. It's important to know: was it delivered, opened, and did it lead to a target action.

FCM returns a MessageId on send, but does not guarantee a delivery callback — by design. For open tracking, custom logic is needed: on notification tap in onMessageReceived or via getInitialNotification() / onNotificationOpenedApp (OneSignal SDK), send an event to analytics with notification_id.

OneSignal provides built-in delivery and CTR analytics. For more detailed analysis — integrate with Amplitude or Mixpanel via webhook on open events. The budget for such a dashboard varies depending on event volume.

How We Implement Push Notifications: Typical Process

1. Audit current implementation — check token storage, update handling, notification types.
2. Design architecture — choose transport (FCM + APNs), segmentation layer (OneSignal/Braze/custom), personalization method.
3. Implementation — write registration code, inbound handling, rich push, deep linking.
4. Testing — send test campaigns, verify delivery on different devices, simulators, regions.
5. Monitoring and analytics — set up dashboard, open and conversion events.
6. Documentation and training — hand over operational materials to the team.

Typical stack: FCM + APNs at transport level, OneSignal or Firebase Notifications Composer for segmentation, custom backend for personalized event-based notifications. For large apps with >1M users, OneSignal has pricing limits — then we use Braze or a custom implementation on AWS SNS.

Timelines depend on complexity: basic FCM+APNs integration with transactional notifications — 1–2 weeks. A full system with segmentation, rich push, analytics, and A/B testing — 4–8 weeks. Order an audit of your current push infrastructure or get a consultation on implementing push notifications in your mobile app — we will contact you within a day and provide an accurate estimate.