AI SMS Agents for Lead Follow-Up: How They Work and How to Choose

An AI SMS agent is software that holds two-way text conversations with your leads. It reads each reply, writes the next text, decides when to follow up, and hands the lead to a person when they're ready. A blast tool sends one message to a list, and an autoresponder sends a canned reply to a trigger; neither reads what the lead wrote back. "Conversational AI SMS" and "SMS AI agent" mean the same thing.

AI SMS agent vs. blast tool, autoresponder and chatbot

	Blast tool	Autoresponder or drip	Website chatbot	AI SMS agent
What starts it	You pick a list and hit send	A trigger: a form fill, a keyword	A visitor opens the chat on your site	A new lead arrives from a form, ad or CRM
Reads replies	No. Replies land in an inbox for a person	Keyword matches at most	Yes, while the visitor is on the page	Yes, every reply
Who writes each message	You, once, for everyone	You, every step, in advance	A script tree or an AI model	The AI, from the lead's details and the conversation so far
Follow-up timing	Whenever you schedule the next send	Fixed delays you set (day 1, day 3, day 7)	None. It ends when the visitor leaves	Decided per conversation, inside allowed hours
Good for	Announcements to an opted-in list	Confirmations and reminders	Questions from people already on your site	Working leads who asked to be contacted, for weeks

A drip sends its day-3 text even if the lead replied "I'm traveling until the 20th." An agent reads that and waits until the 20th.

How a conversation flows

1. A lead comes in with whatever you know: name, phone, source, what they asked about, notes.
2. The agent sends a first text that references what the lead did and asks one easy question. Speed matters here; see why the first minutes count.
3. Each reply is read in context: what's been said, what's still unknown, whether the lead asked to stop.
4. If the lead goes quiet, the agent decides when to try again, and when to stop.
5. When the lead meets your handoff rule, a person takes over with the full thread.

Example exchange

An old website lead who asked about homes in March and never replied. The handoff rule: hand off when the lead says they're ready to look.

What the agent did: it opened with what the lead had asked about, asked one question per text, took "not right now" at face value, picked the next date from what he said and told him, then came back on that date. Each text fits in one SMS segment (under 160 characters; Twilio's limits).

If he had replied "found a place already, please stop texting me," that is an opt-out even though it isn't the word STOP, and the agent must stop texting him.

What it needs to work

• Consent. Get it before the first text, with a form checkbox that names text messages and your business. The FCC's TCPA rules require prior express written consent for automated marketing calls, a signed agreement that names the phone number (47 CFR 64.1200(a)(2) and (f)(9)). The A2P guide has opt-in wording that passes carrier review.
• A2P 10DLC registration. Every local 10-digit business number that sends software texts needs an approved brand and messaging registration. Unregistered numbers are blocked: Twilio returns error 30034. On Twilio, a brand costs $4.50 and vetting a messaging registration $15, and Twilio estimates up to 5 business days for the registration review; the details are in A2P 10DLC registration: cost, timeline and rejections.
• Lead data. At minimum a name and a mobile number. Source, what they asked about and notes are what make the first text specific instead of generic.
• A handoff rule. Write down what "ready" means (asked for a call, gave a timeline, agreed to a showing) and who gets the lead. Without one, the agent either hands off too early or keeps chatting with someone who wanted a person. Include questions it shouldn't answer itself, like a quote, a rate or a legal question: the agent should say a person will follow up, and hand off.

What to check when choosing one

Question to ask	Why it matters
How does a ready lead reach a person, and does the AI stop texting once someone takes over?	Two voices answering the same lead is worse than none.
Does "please stop texting me" count as an opt-out, or only the keyword STOP?	See the next section. Also ask whether an opt-out applies across every campaign and number.
Quiet hours: in whose time zone, and can they be narrowed by state?	Federal rules bar telephone solicitations before 8 AM and after 9 PM at the recipient's location (47 CFR 64.1200(c)(1)). Some states are stricter: Florida bars commercial telephone solicitation calls after 8 PM and limits them to three per 24 hours on the same subject (Florida Statutes section 501.616). Ask a lawyer how these apply to your texts.
Who decides follow-up timing: you, with fixed delays, or the agent, from the conversation?	Test it: reply "check back in March" and see what it does next.
Can you read every conversation as it happens and jump in?	You're responsible for what it says, so you need to see it.
What does it answer if a lead asks "is this a bot?"	Utah requires a business using generative AI in a consumer transaction to disclose it when the person clearly asks (Utah SB 226, 2025, section 13-75-103).
How is it priced?	Per seat, per contact, per conversation or per text. Carriers bill by segment: Twilio charges $0.0083 per segment sent or received on a local number, plus carrier fees of $0.0035 to $0.005 per outbound segment (Twilio US SMS pricing, as of October 2026). Ask whether the price includes the AI, the carrier fees and registration.

One SMS segment holds 160 standard characters, or 153 each when a text is split; one emoji switches the whole text to 70 characters, 67 when split (so can a curly quote, unless Twilio's Smart Encoding straightens it) (Twilio, SMS character limit). So a 200-character reply is 2 segments in plain text and 3 with a single emoji.

Opt-outs: the part keyword filters miss

Under the FCC's rules, a reply of "stop," "quit," "end," "revoke," "opt out," "cancel" or "unsubscribe" revokes consent. Any other wording counts too if a reasonable person would read it as a request to stop. You must honor it within 10 business days, and you may send one confirmation text with no marketing in it; sent within five minutes, it's presumed allowed (47 CFR 64.1200(a)(10) and (a)(12)).

Provider keyword filters are narrower than the rule. Plivo's docs list "Hey, can you stop texting me?" as an example that does not trigger its opt-out block (Plivo DND docs). So the agent itself has to recognize "lose my number" or "not interested, don't text again" and stop. Test it with three or four phrasings before you go live.

Limits

• It texts; it doesn't call. Leads who want to talk need a person, which is what the handoff is for.
• It can say something wrong, and you own it. Utah's law says it is not a defense to a consumer protection violation that generative AI made the statement (13-75-102). Give it accurate facts, and leave quotes, rates and legal or tax questions to a person.
• It can't fix the list. Leads without consent, wrong numbers and landlines stay unreachable.
• It isn't a blast tool. It works one conversation per lead. A one-time announcement to your whole contact list is a different job.

It's a poor fit where every lead needs a long phone conversation before anything happens, or where you can't collect texting consent. To judge whether it's working, track four counts each month: leads texted, leads who replied, handoffs, and opt-outs, and check how many handed-off leads your team actually reached. For how an agent fits with your other follow-up, see AI sales follow-up automation.

If you use Out Nurture

Out Nurture is an AI sales agent that texts your leads in two-way conversations. It uses every detail sent with the lead, decides each reply and when to follow up, and hands ready leads to the salesperson you choose by group text or email summary. You can read every conversation and jump in. STOP and "remove me" are honored immediately across every campaign, and first texts and follow-ups go out only between 8 AM and 9 PM in the lead's time zone. It files your A2P 10DLC registration from inside the app, with carrier fees passed through at cost. The Standard plan is $25 a month with $5 of usage included, then about $0.025 per text with the AI included. Worked example, with assumed volume: 300 leads a month at about 8 texts each is 2,400 texts, or $60 of usage; minus the $5 included, plus the $25 plan, that's about $80 a month. The cost calculator works it out for your volume.