Definition: SMS opt-in consent is a consumer's permission, given through an action like checking a box or texting a keyword, to receive text messages from a named sender for a described program.
Opt-in is the heart of 10DLC review. Carriers want proof that people asked for your texts. Twilio calls opt-in problems a major cause of rejections.
CTIA's 2023 Messaging Principles describe three:
| Message type | Consent level | Example |
|---|---|---|
| Conversational | implied | the consumer texts you first |
| Informational | express | given by text, form, website, or verbally |
| Promotional | express written | signing a form or checking a box online |
CTIA also notes that adding a promotion, like a coupon, to an informational text can make it promotional.
Pulling from CTIA and Twilio:
Federal TCPA rules add that prior express written consent must say the person is not required to agree as a condition of buying anything. This is not legal advice.
Reviewers often check your website to confirm the opt-in you described. Twilio error 30924 says consent language must sit at or next to the checkbox, not in a linked page. See opt-in form requirements.
Related terms: STOP and HELP keywords, Campaign use case, A2P
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CTIA gives checking a box online as an example of express written consent for promotional texts. Providers like Twilio also say the box must be unchecked by default and not required to complete a purchase or signup.
No. CTIA says senders should not use rented, sold, or shared opt-in lists, and that consent is not transferable to another campaign or sender.
CTIA suggests keeping the timestamp, how the person opted in, the language or action used, the campaign, the IP address, the phone number, and who gave consent.
Twilio says verbal opt-in is not enough for marketing, which needs written consent. Telnyx's 2026 guide says verbal opt-ins for marketing need double opt-in.
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