What is an SMS gateway and how to choose one for your business

An SMS gateway is the platform that connects your systems to the mobile network. We explain how it processes each message, when to integrate through an HTTP API or SMPP and what to check before choosing one.

What an SMS gateway is

It is the software that receives the messages your application generates (an OTP code, a payment notice, a campaign), prepares them for the mobile network, delivers them to the operator and returns the result. For your system it is a single sending point; behind it, the gateway handles encoding, queues, retries and reports.

It is the core of A2P (application-to-person) messaging, the kind companies use to notify and verify their customers.

How it processes a message, step by step

1. Your system sends the request with the number, text and sender, via API or SMPP.
2. The gateway validates: international number format, exclusion lists, balance and whether the number is landline or mobile according to Mexico’s National Numbering Plan.
3. It determines the encoding (GSM7 or UCS-2) and how many segments the text needs.
4. It queues and delivers the message to the recipient’s operator.
5. It receives the delivery report (DLR) and sends it to your system by webhook.

We explain it in more detail in how an SMS is delivered, step by step.

HTTP API or SMPP: which to use

There are two common ways to connect to a gateway:

• HTTP API (REST): each message is a request. It is the simplest option to integrate from an ERP, CRM or app, and the one most developers use. See the SMS API integration guide.
• SMPP: the industry-standard protocol for exchanging SMS over a persistent connection. It suits very high volumes or cases where another messaging platform already speaks SMPP.

For most businesses, an HTTP API is enough and easier to maintain. SMPP makes sense when sustained throughput or the existing architecture justify it.

What to check before choosing a gateway

• Documentation and a sandbox to test without sending real messages.
• Per-message delivery reports and real-time webhooks.
• Security: encrypted connections (TLS), content encryption for sensitive messages and IP restrictions.
• Control over encoding and replacement of unsupported characters, so you do not pay for extra segments.
• Capacity and queues to absorb peaks such as paydays or seasonal campaigns.
• Specialized support that responds when something fails in production.

The full list of questions is in how to choose an SMS provider in Mexico.

What about a SIM modem?

Technically, a GSM modem or a phone with a SIM can send SMS from a computer. But that traffic is P2P (person-to-person): it has volume limits, no reliable delivery reports and no brand-name sender, and operators often block lines that send bulk messages. For business use, an A2P gateway is the right choice.

Sources

• 3GPP TS 23.040, Technical realization of the Short Message Service (SMS). 3gpp.org
• SMS Forum, Short Message Peer to Peer Protocol Specification v3.4. smpp.org
• IETF, RFC 8446, The Transport Layer Security (TLS) Protocol Version 1.3. rfc-editor.org

Frequently asked questions