The short answer
They describe the same service from three sides. The SMS gateway is the infrastructure that delivers messages to the mobile networks. Bulk SMS is one way of using it: one message sent to many numbers at once. The SMS API is another way of using it: your own software sending messages through the gateway automatically.
- SMS gateway: the service that connects you to Dialog, Mobitel, Hutch and Airtel and reports delivery.
- Bulk SMS: sending one message to a list or contact group, usually from a web dashboard.
- SMS API: sending from your own website, app or system with an HTTP request, one message or many.
What an SMS gateway does
An SMS gateway sits between you and the mobile networks. It checks and normalises numbers, works out the encoding and segment count, charges the right number of credits, hands each message to the recipient's network and records the delivery report that comes back.
Every SMS a business sends in Sri Lanka goes through a gateway of some kind, whether it is typed into a dashboard or triggered by code. Choosing an SMS gateway Sri Lanka businesses can rely on is the decision that matters; the guide to how an SMS gateway works and how to choose one covers it in detail.
What bulk SMS means
Bulk SMS is the same message going to many recipients in one send: a promotion, a holiday notice, a price change or a reminder to a whole class. You paste numbers or pick a saved contact group, write the message, check the cost and send it now or schedule it.
Because the cost multiplies by every recipient, small details count. A message that spills into a second segment, or Sinhala text that switches to Unicode, doubles the credits for the whole list. What counts as one SMS explains the rules, and the bulk SMS rates show what a campaign costs.
What an SMS API is
An SMS API lets your own software use the gateway without anyone opening a dashboard. A login page sends an OTP, a POS sends a receipt, a delivery system sends a tracking update: each is an HTTP request with a token, a number, a sender name and the text.
The SMS gateway API has a send endpoint, an estimate endpoint that costs a message without sending it, and endpoints to look up delivery status. From API token to your first message walks through a first integration.
Which one do you need?
Most businesses end up using both ways of sending, so the useful question is who sends and when.
- A marketing or operations team sending campaigns and notices: bulk SMS from the dashboard. Start with the bulk SMS campaign checklist.
- A developer sending OTPs, receipts or alerts from an application: the SMS API, as in adding an SMS gateway to a POS or billing system.
- Both: one gateway account covers them, with one credit balance, one set of approved sender names and one delivery log.
Trying it yourself
Create an account, request a sender name and send a test to your own phone from the dashboard. Then generate an API token and send the same message with a single request. Seeing both arrive, with a delivery report for each, makes the difference clearer than any definition.
