· 10 min read
The SMS playbook from the operator's seat
SMS has a 98% open rate, which sounds like a feature until you realise it's also why a bad SMS program burns more goodwill in a week than a bad email program burns in a year. The channel punishes carelessness at a magnitude email doesn't. Here's the operator's view — what to set up, what to write, and the specific mistakes that generate complaints.
Justin Williames
Founder, Orbit · 10+ years in lifecycle marketing
The compliance layer is non-negotiable
98%
SMS open rate. The reason a bad SMS program burns goodwill faster than a bad email program.
160
Character limit per SMS segment. Above this, cost goes up and carriers treat content as higher-risk.
2/wk
Sensible marketing frequency cap for the average SMS subscriber.
A bad SMS program burns more goodwill in a week than a bad email program burns in a year. The channel punishes carelessness at a magnitude email doesn't.
Every SMS program starts with an opt-in architecture. Unlike email, where a soft opt-in through account creation is often defensible, SMS requires express written consent under the TCPA in the US, the PECR in the UK, and the equivalents in most other jurisdictions. "Written" includes a checkbox or keyword reply; it doesn't include buried consent in a terms-of-service document.
The operational requirements that come with that consent: every marketing SMS must include an opt-out mechanism ("Reply STOP to unsubscribe" is the standard). Every opt-out must be honoured within a short window — 10 business days in the US, faster under most EU frameworks. Suppression has to be applied across every channel and every campaign, not just the one the user unsubscribed from.
The part most programs get wrong: proof of consent. If a user ever complains to a regulator, you need to produce the exact moment they opted in — timestamp, IP address, the form they submitted, the text of the consent they agreed to. Most programs don't store this because it lives in a form submission they never bothered to persist. When a regulator asks, "we assume we got consent" is not an answer.
The 160-character medium punishes padding
SMS has a 160-character limit per segment. Messages above 160 characters are sent as multi-part SMS — technically still one message from the user's perspective, but cost per send goes up proportionally and the carrier treats it as higher-risk content.
The discipline the medium imposes: every word has to earn its place. Greetings ("Hi {{first_name}}") consume 20 characters for zero information. Preamble ("We hope you're having a great day") is worse. The operator who writes in SMS first, then translates to email, produces sharper email copy than the one who goes the other direction.
Character discipline applied specifically: lead with the value proposition in the first ten characters, because preview text in most SMS clients shows only the first line. Include a single call-to-action URL, shortened (short links eat less budget and ping-track better). If the message can't work at 120 characters, it probably shouldn't be an SMS.
Frequency is where programs actually fail
Email has implicit frequency tolerance that SMS doesn't share. Two emails in a day is annoying. Two SMS in a day is a reason to opt out. Three emails in a week is fine. Three SMS in a week is aggressive. The delivery gap is smaller because the attention cost is higher — an SMS interrupts; an email waits.
Frequency caps that work in practice: no more than two marketing SMS per week for the average user, with an absolute hard cap of one per day including transactional. Exceptions for time-sensitive events (flash sales, order issues) must be explicit and rare. "Exception" behaviour that happens more than once a month is no longer an exception; it's your baseline cadence, and users will calibrate complaints against it. The cadence guide covers multi-channel frequency governance when SMS is one of several channels reaching the same user.
Honour engagement signals aggressively. A user who hasn't clicked an SMS link in 60 days should be suppressed from marketing SMS — not unsubscribed, but muted. Reactivate on a strong signal (purchase, high-intent action). This keeps the engaged subscriber file small, clean, and deliverable.
What to use SMS for (and what to stop using it for)
SMS is genuinely the right channel for: time-sensitive transactional confirmations, two-factor authentication, delivery notifications, appointment reminders, abandoned-cart nudges where the cart value justifies the send cost, and urgent service alerts. These earn the channel's permission because the value to the user is immediate and clear.
SMS is the wrong channel for: generic marketing promotions that would work equally well in email, newsletter content, product announcements without urgency, and anything that requires more than 160 characters to convey. Using SMS for email-style content doesn't get you better engagement; it gets you opt-outs from users who opted in expecting something different.
The litmus test: would you be willing to wake someone up at 11pm to deliver this message? If no, it doesn't belong in SMS, because the medium always carries some probability of doing exactly that.
Send-time discipline
Time-of-day rules for SMS are stricter than email. Most US states restrict marketing SMS to 8am–9pm local time. The UK's PECR treats outside-hours SMS as per-se unreasonable. These are hard rules — a single send that arrives at 11pm local will generate complaints and can attract regulator attention if it becomes a pattern.
Respect local time zones, not the sender's timezone. A scheduled send that fires at 9am PST hits subscribers in New York at noon, which is fine, but the same send fires in Sydney at 3am local, which is a disaster. Every SMS program needs timezone-aware send scheduling at the profile level, and every test plan needs to include a profile in a distant timezone to catch this before it hits production.
The Orbit SMS Playbook skill covers the full compliance + operational architecture, including the timezone scheduling patterns that actually work in Braze and the suppression logic that keeps engagement clean.
Frequently asked questions
- Do I need explicit opt-in for marketing SMS?
- Yes. TCPA in the US, PECR in the UK, CASL in Canada, and the EU ePrivacy directives all require express consent for marketing SMS. A checkbox or keyword reply counts as 'written'; a general terms-of-service acceptance doesn't. Store the timestamp, IP, and form text of every opt-in — regulators will ask.
- What's the right SMS frequency for marketing?
- For most programs: no more than two marketing SMS per week, with a hard cap of one per day including transactional. SMS has lower frequency tolerance than email because the attention cost is higher — each message interrupts rather than waits. Programs that exceed this generate opt-outs faster than they add subscribers.
- Can I send marketing SMS outside business hours?
- Most US states restrict marketing SMS to 8am–9pm local time. The UK's PECR treats outside-hours marketing as unreasonable per se. Always use local-timezone scheduling at the profile level, not the sender's timezone — a 9am PST send arrives in Sydney at 3am local, which is a compliance incident.
- Should SMS opt-outs suppress email too?
- Best practice is yes — an unsubscribe on any channel should suppress marketing across all channels, unless the user has explicitly opted to remain on others. Channel-specific suppressions are legally defensible in most jurisdictions but create a worse user experience and higher long-term complaint rates.
- What's the character limit for SMS?
- 160 characters per segment. Messages over 160 are sent as multi-part SMS — technically one message to the user but costs multiply by segment count and carriers treat higher-segment messages as higher-risk. Aim for under 120 characters as a working target; if the message can't work at that length, it probably shouldn't be SMS.
- What's the right use case for SMS vs email?
- SMS for time-sensitive transactional content: confirmations, 2FA, delivery notifications, appointment reminders, urgent service alerts, high-value abandoned-cart. Email for everything else — newsletters, promotional content, education. Using SMS for content that could be email produces opt-outs, not better engagement.
This guide is backed by an Orbit skill
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