SMS Broadcast API and Software: How Business Texting Works

SMS Campaign Engine: Free Open Source SMS Broadcast Software

SMS Campaign Engine is the open source release of SMS Broadcast, the same engine that runs our hosted texting app on this site. The full source code is free on GitHub under the MIT license, which means you can download it, run it on your own hosting, and send from your own server with no monthly platform fee. You pay only your SMS provider's per message rates, and your subscriber list lives on your own server instead of inside someone else's platform.

In plain terms, here is what it does. You load in your contacts, write your messages, and the engine handles the sending. Broadcasts are spread across the day in hourly batches instead of being dumped all at once, and each message goes out at a sensible local time for the person receiving it. Drip campaigns send an automatic series of texts on a daily, weekly, or monthly rhythm to each new subscriber. Replies of STOP unsubscribe people automatically, and that suppression list is permanent, so nobody who opted out ever gets another message even if you re-import an old file. Every link click is counted, bots are filtered out of the numbers, and the engine keeps a profile on each contact so your most engaged subscribers get priority when a campaign fills up.

It works with 12 SMS providers, including Twilio, Telnyx, Vonage, Plivo, Sinch, Bandwidth, ClickSend, and TextMagic, all through one send screen and one API. You bring your own provider account, which keeps you in control of your per message cost, and you can switch providers without losing your list or your history. Everything is managed from a simple admin area in the browser: sending numbers, messages, lists, drip series, contacts, and daily reports.

The whole thing is one small app that runs on almost any hosting, including cheap shared hosting, and it stores its data in a single file, so there is no database server to set up. If you would rather not run your own server at all, the hosted SMS Broadcast app gives you the same engine fully managed, just contact our team to get set up. Either way you are using the same proven sending engine, the only difference is who runs it.

Step by Step Guides and Documentation

These guides walk through the most common jobs, from sending your first bulk text campaign to wiring up AI powered replies. They are written for SMS Campaign Engine, and since the hosted SMS Broadcast app runs the same engine, the concepts carry over either way.

What Is an SMS Broadcast System

An SMS broadcast system is software that sends text messages to a list of subscribers on your behalf. At the simplest level, you write a message, select an audience, and the system delivers it through a carrier network to every phone on that list. Most platforms also handle replies, manage opt outs, schedule messages for later, and track delivery and engagement metrics.

The system sits between your business and a telecom provider like Twilio, Vonage, or Telnyx. You do not send messages directly through a carrier. Instead, the platform connects to a provider's API, which handles the actual delivery across carrier networks. This means your choice of platform and your choice of provider are two separate decisions, and getting both right matters.

Businesses use SMS broadcasts for promotional campaigns, appointment reminders, shipping notifications, flash sales, event announcements, and customer re-engagement. The format works because the message lands in a place people already check constantly, their phone's native messaging app, with no algorithm deciding whether to show it.

Why SMS Outperforms Other Marketing Channels

The numbers behind SMS marketing are difficult to argue with. Text messages see open rates between 90% and 98%, compared to 20% to 25% for email. Most texts are read within three minutes of delivery. Click through rates on links in text messages run five to ten times higher than email campaigns targeting the same audience.

The reason is simple. People have trained themselves to ignore most email. Inbox tabs, spam filters, and sheer volume mean that even well crafted emails get buried. Text messages arrive in a space with far less competition. A phone buzzes, the preview text appears on the lock screen, and the recipient reads it whether they meant to or not.

SMS also reaches people who do not use email actively. Older demographics, blue collar workers, and service industry employees are often easier to reach by text than by any other digital channel. For businesses in retail, restaurants, healthcare, and local services, this matters enormously. Your best customers might never open a marketing email, but they will read every text you send as long as you do not abuse the channel.

That said, SMS is not a replacement for email. The two work best together. Email handles long form content, detailed offers, and nurture sequences. SMS handles urgency, reminders, and time sensitive promotions. The businesses that get the best results combine both channels in coordinated campaigns rather than treating them as separate efforts. If you run both, our email broadcast software is the same engine adapted for email, and the two share the same API style.

Types of SMS Messages

Not all text messages serve the same purpose, and the legal rules differ depending on the type you are sending.

Promotional messages are marketing. Flash sales, discount codes, new product announcements, event invitations. These require explicit opt in consent from the recipient and must include a way to opt out. Promotional messages are what most people mean when they talk about SMS marketing, and they are the most heavily regulated category.

Transactional messages are triggered by something the customer did. Order confirmations, shipping updates, appointment reminders, password resets, payment receipts. These are expected communication tied to a specific action, and the compliance requirements are lighter because the customer initiated the relationship. They still need to come from a registered number and follow carrier guidelines, but you do not need the same level of marketing consent.

Conversational messages are two way exchanges. A customer texts a question, your system or your team replies. This includes customer support over SMS, AI powered auto replies, and sales conversations. Conversational messaging turns SMS from a broadcast channel into a communication channel, and it is where much of the innovation in the space is happening right now.

Features That Matter When Choosing a Platform

Every SMS platform will let you send a message to a list. The differences show up in everything around that core action.

Contact management and segmentation. You need to organize subscribers into groups based on behavior, location, purchase history, or any other attribute that makes targeting possible. A platform that only lets you blast your entire list is barely better than doing it manually. Good segmentation is what separates SMS marketing from SMS spam.

Scheduling and automation. Sending messages at the right time matters more than most businesses realize. A flash sale announcement at 2 AM gets ignored. The same message at 11 AM on a Tuesday gets clicks. Look for platforms that support scheduled sends, timezone aware delivery, and automated drip sequences triggered by subscriber actions.

Provider flexibility. Some platforms lock you into a single SMS provider. Others let you connect your own provider account, which gives you control over per message costs and lets you switch providers if deliverability drops or pricing changes. Provider flexibility also matters for carrier based routing, where you send messages through different providers depending on the recipient's carrier to maximize delivery rates.

Delivery tracking and analytics. You need to know which messages were delivered, which failed, which were clicked, and which triggered opt outs. Without this data, you are guessing. Good platforms track delivery status per message and per carrier, so you can catch deliverability problems before they affect an entire campaign. Click tracking on links tells you which messages actually drive action.

Compliance tools. Automatic STOP handling, opt in confirmation, consent record keeping, and quiet hours enforcement. These are not optional features. They are legal requirements, and the platform should handle them automatically rather than making you manage compliance manually.

Two way messaging. If a customer replies to your text, can the platform handle it? Can it route the reply to a person, trigger an automated response, or feed it into a support queue? One way blasting is useful but limited. Two way SMS turns the channel into a real conversation, which builds the kind of customer relationship that drives repeat purchases.

Choosing an SMS Provider

The provider is the company that actually transmits your messages across the carrier network. The platform is the software you use to manage campaigns. Some companies are both, but understanding the distinction helps you make better decisions about cost and reliability.

Major providers include Twilio, Vonage, Plivo, Sinch, Telnyx, Bandwidth, ClickSend, and TextMagic. They differ in pricing per message, geographic coverage, carrier relationships, API reliability, and support quality. Most charge somewhere between half a cent and two cents per message in the US, with international rates varying widely.

The cost per message is the obvious comparison point, but it is not the only one. Deliverability matters more. A provider that charges a quarter cent less per message but gets filtered by carriers 15% of the time is not actually cheaper. Carrier filtering is a growing problem, and providers with strong carrier relationships and proper registration processes will get more of your messages through.

If your platform supports multiple providers, you can route messages through different providers based on the recipient's carrier. This is called carrier based routing, and it can meaningfully improve delivery rates for high volume senders. You send T-Mobile subscribers through one provider and Verizon subscribers through another, using whichever provider has the best delivery rate for each network. SMS Campaign Engine supports all of the providers named above through one send API, and our guide on connecting an SMS provider walks through the account setup for each one.

SMS Broadcast APIs: Sending From Your Own Software

An SMS broadcast API is the developer facing version of everything described above. Instead of logging into a dashboard to create a campaign, your own application calls the API to send messages, manage subscribers, and check delivery status programmatically. The providers covered earlier, Twilio, Vonage, Plivo, Telnyx, and the rest, all expose APIs, and most broadcast platforms offer an API layer on top of their own features as well.

The distinction matters because the two serve different users. Broadcast software is built for marketers, a person writes a message, picks a segment, and hits send. An API is built for developers who want texting to happen inside their own product or workflow. An order ships and your system texts the tracking number automatically. A booking is made and the confirmation goes out without anyone touching a dashboard. An AI agent handles a support conversation and sends the follow up itself. If the message should be triggered by an event in your software rather than a person planning a campaign, you want the API.

What to evaluate in an SMS broadcast API. Documentation quality comes first, because a poorly documented API costs you development time on every feature. After that, look for delivery status webhooks so your system knows whether each message actually arrived, which is the API equivalent of the deliverability tracking a dashboard gives you. Check the throughput limits, since API sending speed is still governed by your 10DLC trust score and carrier rules, not by how fast you can make requests. And confirm the API includes subscriber and opt out management endpoints, because every compliance rule in the next section applies to API sends exactly as it does to dashboard sends. STOP replies must still be honored automatically, consent is still required, and quiet hours still apply.

Most businesses do not have to choose between software and an API. The practical setup is a platform that offers both, marketers run planned campaigns from the dashboard while the API handles transactional and event driven messages from your own systems, all sharing one subscriber list, one consent record, and one set of opt outs. SMS Campaign Engine works exactly this way: the admin area covers campaign work in the browser, and the same install exposes a JSON API for sends, subscriber management, drip enrollment, opt outs, and campaign scheduling. The full API reference documents every endpoint with examples.

Compliance and Legal Requirements

SMS marketing is regulated more heavily than email. The penalties for violations are real, carriers actively filter non compliant senders, and getting it wrong can permanently damage your ability to send messages.

In the United States, the Telephone Consumer Protection Act (TCPA) requires prior express written consent before sending marketing texts. This means the recipient must actively agree to receive messages from you, typically through a web form, a keyword opt in, or a written signature. Pre checked boxes do not count. Buying a phone number list and blasting it is illegal and will result in fines of $500 to $1,500 per message.

The 10DLC registration system is the carrier industry's framework for business text messaging. Every business sending SMS through a standard 10 digit phone number must register their brand and campaign type with The Campaign Registry. This process verifies your identity, describes the type of messages you plan to send, and assigns a trust score that directly affects your sending throughput and filtering rates. Skipping registration means your messages get throttled or blocked entirely.

Every message must include a way to opt out. The industry standard is replying STOP to unsubscribe. Your platform must process these automatically and immediately. Sending another marketing message to someone who replied STOP is a TCPA violation regardless of whether you saw the reply. The consent rules are strict, but they exist because consumers demanded them, and following them actually improves your results by ensuring you only message people who want to hear from you.

Building and Managing Your Subscriber List

Your subscriber list is the entire foundation of SMS marketing. A list of 500 people who genuinely want to hear from you will outperform a list of 50,000 scraped numbers every single time, because engagement drives deliverability and deliverability drives results.

The most effective way to build a subscriber list is through your existing customer touchpoints. Add an SMS opt in checkbox to your checkout flow, your appointment booking form, your account registration page, and your email signup forms. Offer something immediate in exchange for subscribing, a discount code, early access to a sale, or a free resource. People are protective of their phone numbers, so the value exchange has to be obvious.

Keyword opt ins work well for in person businesses. A sign at the register that says "Text JOIN to 55555 for 15% off your next visit" converts foot traffic into subscribers with zero friction. The customer sends a text, receives an auto reply with the discount and a confirmation of their subscription, and you have a new subscriber who is standing in your store right now.

List hygiene is just as important as list growth. Remove numbers that consistently bounce. Watch for subscribers who never open or click anything after several months, and consider a re-engagement campaign before removing them. Importing contacts from a CSV is fine for migrating between platforms, but every number on that list must have existing consent documentation. Importing a purchased list will get your account shut down by any reputable provider.

Two Way Messaging and AI Replies

Broadcasting is only half of what SMS can do. When a customer texts back, that reply is an opportunity. They might be asking a question about your product, confirming an appointment, responding to an offer, or requesting support. How you handle that reply determines whether SMS becomes a one way megaphone or a genuine communication channel.

Traditionally, two way SMS meant routing replies to a person who would type back manually. That works at low volume but breaks down fast. Modern platforms use AI powered replies that can handle common questions automatically, escalate complex issues to a human, and maintain conversation context across multiple messages. The customer gets an instant response at any hour, and your team only gets involved when the AI cannot handle it confidently.

This is where SMS and AI customer service intersect. A customer texts asking about their order status. The system looks up their order, finds the tracking information, and replies with it in seconds. No human involved, no wait time, no support ticket. For businesses handling dozens or hundreds of inbound texts per day, automated two way messaging turns SMS from a cost center into something that scales without adding headcount.

SMS Campaign Engine has this built in. Point one of your sending numbers at a chat bot and incoming replies get answered automatically by text, using your own knowledge base to keep the answers accurate. Our guide to AI text message auto replies shows how to set it up.

Measuring Campaign Performance

The core metrics for SMS campaigns are delivery rate, open rate, click through rate, opt out rate, and conversion rate. Delivery rate tells you whether messages are actually reaching phones. Click through rate tells you whether the content is compelling enough to drive action. Opt out rate tells you whether you are sending too often or sending the wrong content.

A healthy SMS campaign has a delivery rate above 95%, a click through rate between 10% and 30%, and an opt out rate below 2% per campaign. If your opt out rate spikes, you are either messaging too frequently, targeting the wrong segment, or sending content that does not match what subscribers signed up for.

Measuring ROI requires connecting SMS activity to actual revenue. This means tracking which clicks led to purchases, which coupon codes were redeemed, and which appointment reminders reduced no show rates. Attribution is messier than email because many SMS conversions happen offline, a customer reads a text about a sale and walks into the store an hour later, but even imperfect tracking gives you enough signal to know which campaigns are working and which are not.

If you run both email and SMS campaigns, split testing across channels helps you understand which messages work better as texts and which work better as emails. Some offers convert better in SMS because of the urgency factor. Others need the extra space that email provides to explain the value.

Common Mistakes That Kill SMS Campaigns

Sending too often. Email subscribers tolerate daily messages. SMS subscribers do not. For most businesses, two to four messages per month is the right frequency. Retail during holiday season might push to weekly. Anything more than that and your opt out rate will climb fast. Every subscriber you lose to over messaging is someone who was interested enough to opt in and then got annoyed enough to leave.

Ignoring carrier filtering. Carriers like T-Mobile and AT&T actively filter messages they consider spam or non compliant. If your messages are getting blocked, it is usually because your number is not properly registered, your content triggers spam patterns, or your sending volume exceeds your trust score. The fix is almost always better registration and slower ramp up, not switching providers.

No segmentation. Sending every message to your entire list is the fastest way to burn through subscribers. A 25 year old in Austin and a 55 year old in Chicago do not want the same message at the same time. Even basic segmentation by purchase history, location, or signup source dramatically improves engagement and reduces opt outs.

Weak calls to action. A text message gives you 160 characters to get someone to do something. "Check out our new collection" is vague and ignorable. "Flash sale, 40% off all jackets until midnight, shop here: [link]" tells the reader exactly what to do and why to do it now. Every SMS should have a clear, specific, time bound reason to act.

Not having a fallback plan. Carriers go down. Providers have outages. Registration gets delayed. If your entire marketing strategy depends on SMS working perfectly every day, you need a backup channel. The businesses that combine SMS and email effectively have resilience built in, if one channel has a bad day, the other picks up the slack.