SMS opt-in language builder

The opt-in confirmation is the message with a fixed list. CTIA's Messaging Principles ask for “(1) the program name or product description; (2) customer care contact information (e.g., a toll-free number, 10-digit telephone number, or HELP command instructions); (3) how to opt-out; (4) a disclosure that the messages are recurring and the frequency of the messaging; and (5) clear and conspicuous language about any associated fees or charges and how those charges will be billed” (§ 5.1.2.1), and it goes out before any other message. Twilio's 10DLC guide says campaigns are vetted so everything “aligns with carrier requirements and CTIA guidelines,” which is why the campaign form asks for the exact wording of each reply (the 10DLC registration checklist covers the rest of that form).

For a keyword campaign, Twilio's 10DLC guide adds that “the welcome message sent after the customer texts the keyword must contain all required disclosures before any other content is sent.” The reply to HELP needs less: CTIA's short code handbook asks senders to answer it “with the Program name and further information about how to contact the Message Sender” (§ 3.4). The opt-out reply is “one final opt-out confirmation message per campaign” (Principles § 5.1.3).

For marketing texts the call to action also says consent is not a condition of purchase. That line comes from the FCC's definition of prior express written consent, which must disclose that “the person is not required to sign the agreement (directly or indirectly), or agree to enter into such an agreement as a condition of purchasing any property, goods, or services” (47 CFR § 64.1200(f)(9)(i)(B); see prior express written consent). A web sign-up form carries the same parts next to the phone field; the SMS consent form template writes that version.

The checks read words, not intent: they look for the brand you typed, an opt-out instruction with STOP, a rates line. A message can pass every check and still confuse a customer, so read each one as the person receiving it would.

One SMS carries 140 bytes: 160 characters in the GSM-7 alphabet, or 70 in UCS-2, the encoding a phone switches to for any character outside it. A longer text is split into segments, and each loses seven characters to the header that puts it back together, so a part holds 153 GSM-7 or 67 UCS-2 characters. Twilio, which bills per segment, notes one exception: multi-segment toll-free texts to the US or Canada carry 152 and 66 per part (the 10DLC vs toll-free guide covers the routes).

The trap is punctuation. The default confirmation above is 155 characters and 1 segment. Paste it from a word processor that curls the apostrophe in “you're” and the whole message turns UCS-2: 3 segments of up to 67 characters for the same words. The builder names the character that did it and offers a one-click swap to plain punctuation. Characters from the GSM-7 extension table, such as € [ ] { } ^ ~ |, stay GSM-7 but count as two. For any message beyond these five, the SMS segment counter shows where each segment breaks, and Twilio SMS pricing explained turns segments into a bill.

Under the FCC's rule a customer may revoke consent “by using any reasonable method,” and a reply with any of seven words is a reasonable method per se, honoured “within a reasonable time not to exceed ten business days from receipt” (47 CFR § 64.1200(a)(10)). Other words count too “if a reasonable person would understand those words to have conveyed a request to revoke consent.” CTIA asks senders to act on plain-language requests and to ignore “de minimis variances” such as capitalization and punctuation (§ 5.1.3).

Every rule and figure the builder encodes, with the date it was read. Twilio's guide is one provider's reading of the carrier rules; your own provider's campaign form may word a field differently. This is a drafting aid, not legal advice.