Bulk SMS & SMS API
Bulk SMS that delivers — OTPs, alerts and campaigns at scale
Send transactional, OTP and promotional SMS worldwide — from our campaign platform or a clean REST API, with a delivery receipt for every message.
Delivery receipts · Global carrier reach · Volume pricing
Routes
Transactional vs promotional vs OTP routes
Bulk SMS isn't one pipe. Each route has different sender rules, consent requirements and delivery behaviour — using the right one is what keeps delivery rates high.
| Transactional | OTP | Promotional | |
|---|---|---|---|
| Typical use | Order updates, alerts, reminders | Login and payment verification codes | Offers, sales, re-engagement |
| Sender ID | Registered alphanumeric ID | Registered alphanumeric ID | Registered ID, promo-flagged |
| Consent | Implied by relationship | Implied by the transaction | Explicit opt-in required |
| Delivery window | 24/7 | 24/7, highest priority | Business hours recommended |
What is a bulk SMS service?
A bulk SMS service lets a business send text messages to many recipients at once — from a few hundred delivery alerts a day to millions of campaign messages — through carrier-grade connections rather than a phone. Messages are sent from a registered sender ID, tracked with delivery receipts (DLRs), and billed per message part.
You can send two ways: through the web platform (upload contacts, pick a template, schedule, track) or through the SMS API, which drops sending into your own software — OTPs at signup, alerts on order events, reminders before appointments.
SMS remains the one channel that reaches every mobile handset on earth — no app installs, no internet connection, no operating-system dependency. That's why it's still the backbone for OTPs and critical alerts even in app-first businesses.
SMS API
An SMS API developers actually like
One POST to send, a webhook for delivery receipts. Idempotent requests, sensible errors, and the same shape as our WhatsApp and RCS APIs.
curl -X POST https://api.hostmentor.com/v1/sms \
-H 'Authorization: Bearer $API_KEY' \
-d to='+919800000000' \
-d sender='HSTMTR' \
-d template='otp_login' \
-d vars='{"code":"728194"}'const res = await hostmentor.sms.send({
to: '+919800000000',
sender: 'HSTMTR',
template: 'otp_login',
vars: { code: '728194' },
});$client->sms->send([ 'to' => '+919800000000', 'sender' => 'HSTMTR', 'template' => 'otp_login', 'vars' => ['code' => '728194'], ]);
Message parts
How many characters fit in one SMS?
SMS is billed per message part, and the part size depends on encoding. One emoji switches the whole message to Unicode and more than halves the capacity — worth knowing before you write the template.
Standard SMS (GSM encoding)
160 characters per message
“Your order has shipped. Track it at hstm.co/t/4821” — 51 chars, 1 part
Unicode SMS (emoji / special characters)
70 characters per message
“Your order has shipped 📦 Track: hstm.co/t/4821” — Unicode, 2 parts
Longer messages are split and each part is billed as one SMS. Concatenated (multi-part) messages carry a stitching header, so parts hold 153 GSM / 67 Unicode characters. Our platform shows a live part count as you type.
Platform features
Everything a serious SMS operation needs
The platform features that separate a campaign tool from a toy.
Scheduling & throttling
Send now, schedule for later, or drip at a controlled rate so replies don't swamp your support team.
Personalization
Merge variables per recipient — names, order numbers, amounts — from your upload or API payload.
Two-way & keywords
Receive replies on long codes, run STOP/HELP keywords automatically, and route inbound messages to webhooks.
Link tracking
Branded short links with per-recipient click tracking, so SMS campaigns report like email campaigns.
Real-time DLR webhooks
Delivery receipts stream to your endpoint the moment carriers confirm — no polling, no batch files.
Contacts & segments
Lists, custom fields, deduplication and consent flags managed in the platform or synced via API.
Use cases
Where bulk SMS earns its keep
The highest-volume SMS use cases across our customers.
Banking & fintech
Transaction alerts, OTPs and fraud warnings — the messages that must always arrive.
E-commerce & D2C
Order confirmations, shipping updates and cart-recovery nudges that convert.
Logistics
Pickup, out-for-delivery and proof-of-delivery notifications for drivers and customers.
Healthcare
Appointment reminders, report-ready alerts and follow-up scheduling.
SaaS & apps
Login OTPs, security alerts and usage notifications straight from your backend.
Travel & hospitality
Booking confirmations, gate changes and check-in reminders in real time.
Compliance
Sender registration, made easy
Most destinations require registered senders — alphanumeric IDs, and in the US, 10DLC campaign registration. Unregistered traffic gets filtered. We walk you through every step.
Pick your sender
Choose alphanumeric sender IDs or numeric long codes per destination country.
Register where required
We file sender-ID registrations and US 10DLC campaigns on your behalf.
Set up opt-in
Consent language and unsubscribe handling that satisfies GDPR, TCPA and local rules.
Send with confidence
Registered routes mean higher throughput and delivery rates from day one.
Already registered elsewhere? Bring your sender IDs — we'll migrate the setup.
Simple per-part pricing
SMS is billed per message part, priced by destination country, with volume tiers that reward scale. No platform fee to start.
- Billed per part: 160 GSM / 70 Unicode characters (153/67 when multi-part)
- Rates vary by destination and route type
- Delivery receipts and analytics included on every route
- Volume slabs — the more you send, the less each part costs
FAQ
Bulk SMS questions, answered
Character limits, routes, registration and delivery — the details that decide campaigns.
How many characters can one SMS have?
160 characters with standard GSM encoding, or 70 characters if the message contains Unicode (emoji or special scripts). Longer messages split into parts — 153 GSM / 67 Unicode characters each because of the stitching header — and each part is billed as one SMS.
What is an SMS API?
A web API that lets your software send SMS programmatically — your backend makes an HTTP request, and we handle carrier routing, retries and delivery receipts. It's how OTPs, alerts and reminders get sent automatically at any scale.
What's the difference between transactional and promotional SMS?
Transactional SMS covers operational messages (OTPs, order updates) tied to an existing relationship and delivered 24/7. Promotional SMS is marketing — it requires explicit opt-in and unsubscribe handling, and many carriers apply stricter filtering to it.
Do I need to register a sender ID?
For most destinations, yes. Alphanumeric sender IDs need pre-registration in many countries, and US traffic requires 10DLC campaign registration. We handle the filings — registered routes get materially better delivery rates.
How fast are OTP SMS delivered?
OTP routes are the highest-priority SMS class, typically delivering within a few seconds. Every message returns a delivery receipt with a timestamp, so you can measure your real p95 latency rather than trust a brochure number.
Can I schedule and personalize campaigns?
Yes. The platform supports contact lists, merge variables per recipient, scheduled and throttled sends, and link tracking — or drive all of it from the API if you'd rather keep logic in your stack.
Can I send international SMS?
Yes — routes cover 190+ destination countries with per-country rates and local sender rules handled per destination. One API, one account, worldwide delivery.
What sender ID will my messages show?
Where the destination supports it, a registered alphanumeric sender (your brand name); elsewhere a dedicated long code or shortcode. We configure the right sender type per destination during onboarding.
Start sending SMS today
Tell us your destinations and volumes — we'll send the rate card the same day.
Volume pricing · No lock-in