AI SMS Chatbot for Business: How It Works, What Carriers Require, What It Costs

What is an SMS chatbot?

An SMS chatbot is a program connected to a business phone number that reads incoming texts and replies to them. It lives on the number, not in an app. The customer texts a number they already have and gets the answer in the same thread, without installing anything or creating an account.

There are two kinds. A keyword bot works like a phone menu. It waits for YES, NO, STOP or "reply 1 for hours" and sends a reply you wrote in advance. An AI SMS chatbot passes the customer's text to a language model, which reads the question in whatever words the customer used and writes an answer. It can carry a conversation over several messages, as long as your system keeps what was said before.

The two can share one number. Fixed keywords handle opt-out and help requests, and the model handles the rest.

Conversational AI over SMS vs keyword bots

Conversational SMS just means two-way texting. The other side can be a person, a bot, or a bot that passes the thread to a person when it gets stuck.

Vendors disagree on which kind of bot suits SMS. ChatBot.com argues that "texting has no buttons or menus to lean on, so SMS punishes the rule-based approach harder than any other channel." Infobip, in a March 2024 post, says rule-based bots "are the quickest and easiest to set up" and that conversational bots, given "the relative cost and speed of typing text on a mobile device", are "better suited for web and chat app channels." Both are vendor opinions.

The table is our reading of the tradeoff, not a vendor benchmark.

How an AI SMS chatbot works: number, SMS API, LLM and memory

Follow one message. A customer texts your number. The carrier hands the text to your SMS provider, for example Twilio or Telnyx. The provider sends it to your application as a webhook, an HTTP request to a URL you set. Your application looks up earlier messages from that phone number, adds them to the prompt along with your rules and content, and sends it to the language model. The model's answer goes back out through the provider's API to the customer's phone.

SMS keeps no session. Each text arrives on its own, with a phone number attached. If the bot should remember that this customer asked about a refund yesterday, your system has to store the thread by phone number and send the relevant part to the model every time. The same store is where opt-out status, consent records and notes for a human handoff belong.

Opt-out replies reach your application as well. Twilio's help article on opt-out keywords says: "When Twilio receives one of these replies, we will create a 'block list' entry on our side, and then pass the message on to your webhook." Your code can then mark the number as unsubscribed in its own records.

What can an SMS chatbot automate? Examples by business type

Each item below is one job a text bot can take on. We left out outcome numbers on purpose: none of the vendor pages we read publishes a measured resolution or accuracy rate for SMS bots.

If you're still deciding where to start, our list of business processes worth automating first includes customer conversations over SMS.

• After-hours lead reply: someone texts a question at night, the bot answers, asks what they need and offers a time to talk.
• Appointment confirmation: the bot sends the reminder, reads "can we do Thursday instead?" and passes the request to your booking tool or your team.
• Ecommerce: order status and returns questions by text, answered from your order data and your returns policy.
• FAQ answers from your own content: hours, service areas, what to bring, how a process works.
• Subscriptions: a customer starts, pauses or cancels a recurring service inside the same text thread.
• Handoff to a person: when the bot can't answer, it passes the whole thread to your team, so the customer doesn't repeat themselves.
• When the bot has to act in other systems, such as updating a CRM record, taking a payment or changing an order, it is closer to an AI agent than a chatbot.

Before the first text: A2P 10DLC registration, opt-in and STOP

This section covers the US only. Twilio defines A2P 10DLC as "the standard that United States telecom carriers have put in place to ensure that SMS traffic to US end users through long code phone numbers is verified and consensual." Anyone texting from an application through a 10-digit number must register, Twilio says, "individuals and hobbyists" included.

Registration has two parts. The brand says who is sending, and the campaign says what you send and how people opt in, opt out and get help. You register through your SMS provider, not directly with The Campaign Registry (TCR). Twilio's fees, checked 15 October 2026: $4.50 one-time for a Sole Proprietor or Low Volume Standard brand, or $46 for a Standard brand, which includes $41.50 of secondary vetting. Each campaign costs a $15 vetting fee that isn't refundable, then $1.50 to $10 a month depending on the use case. On 1 August 2025 TCR raised brand registration from $4.00 to $4.50 and standard vetting from $40.00 to $41.50, so older guides still quote the lower numbers.

Plan for the wait. Twilio's own pages give three campaign review times: up to 5 business days, about 7, and up to 10 while submission volumes are high. A campaign can't send on the A2P route until it's approved. Senders who skip registration "will receive additional carrier fees for sending unregistered traffic", Twilio says, but the pages we read don't give the amount. Toll-free and short-code numbers sit outside 10DLC, and toll-free has its own verification.

Consent comes before the texts. The FCC's TCPA rule (47 CFR 64.1200) treats a text message as a call, and it requires "prior express written consent" for telemarketing calls made with an autodialer or an artificial or prerecorded voice. An electronic signature counts, and the agreement has to say that signing isn't a condition of buying anything. CTIA, the wireless industry association, asks senders to record when and how each person opted in. For recurring messages, it asks for a confirmation text that says how to opt out and how often messages will come.

Opt-out is where an AI bot has more work to do. The FCC rule says a reply using "'stop,' 'quit,' 'end,' 'revoke,' 'opt out,' 'cancel,' or 'unsubscribe'" revokes consent. Other wording counts too, "if a reasonable person would understand those words to have conveyed a request to revoke consent." Requests must be honored within ten business days. One confirmation text with no marketing in it is allowed, and if it goes out within five minutes it's presumed to fall within the original consent.

Twilio's default handling covers part of that. On long-code and toll-free numbers it blocks the sender after STOP, STOPALL, UNSUBSCRIBE, CANCEL, END, REVOKE, OPTOUT or QUIT, and sends its own unsubscribe confirmation. But in Twilio's words, "only single-word messages will trigger the block": "STOP PLEASE" won't. The block applies only to the number that last texted the customer, and short codes aren't handled by default. Note also that the FCC list has "opt out" as two words, while Twilio's list has OPTOUT as one.

Our reading, not legal advice: a bot that reads free text should catch "please stop texting me" and mark the number itself, across every number you send from. CTIA's guidelines say opt-out requests in normal language, such as "please opt me out", "should also be read and acted upon." For TCPA questions, ask a lawyer. Twilio gives the same advice: "consult with your legal counsel".

If the texts carry patient information, your SMS provider is one more vendor in the data path. Our notes on HIPAA-compliant automation tools explain why each vendor on that path needs its own BAA.

What does an SMS chatbot cost to run?

Running costs come in four parts: the provider's rate per segment, a carrier fee on top, the phone number, and registration. The table uses list prices from Twilio and Telnyx, checked 15 October 2026. Both say they pass carrier fees through without a markup.

Texts are billed per segment, not per message. A plain-text (GSM-7) segment holds 160 characters. Once a text is split, each part holds 153. One emoji or one Chinese character switches the whole text to UCS-2, and the limit drops to 70 characters, then 67 per part. That matters for an AI bot, because models write long. A 400-character answer is three segments and costs three times a short one. Twilio accepts up to 1,600 characters, which is 11 segments: 11 × $0.0083 = $0.0913 before carrier fees.

Here is our arithmetic from the list prices, not a vendor quote. One outbound, one-segment text on a Twilio local number costs $0.0083 + $0.0035 = $0.0118 to an AT&T phone, $0.0128 to T-Mobile and $0.0133 to Verizon. On Telnyx to AT&T it's $0.004 + $0.0035 = $0.0075. Year one of registration for one Twilio local number, before any texts: $51.30 with a Low Volume Standard brand and a low-volume mixed campaign, or $194.80 with a Standard brand and a standard campaign. Both assume the campaign stays active all year.

The language model's cost per reply isn't in the table. It depends on the model and on how much conversation history you send with each message, so check your model provider's pricing page.

Building the bot is a separate, one-time cost. Our guide to what an AI chatbot costs to build covers that side.

SMS chatbot platform or a custom build?

Start from what the bot has to do. This isn't a ranking of platforms.

Two platforms describe SMS support on their own pages. Crisp says you can "connect ChatGPT, Claude, Mistral, Gemini, or Crisp self-hosted models" and "step into the conversation at any time and take over", and it offers a 14-day free trial with no card required. ChatBot.com says its bot "hands the conversation to your team when it counts", that "opt-out handling and country permissions live in your Twilio Console", and that you pay two bills: the ChatBot.com plan and Twilio's message rates. We didn't check either platform's plan prices.

• A platform fits when the answers come from an FAQ or help content, the bot only talks, and a person takes over everything else.
• A custom build fits when the bot has to remember a customer across days, read or write your CRM, take payments or manage subscriptions, or run on a model you pick and host.
• Either way, ask whose account holds the phone number and the 10DLC brand and campaign, and what happens to them if you switch.

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