SMS marketing delivers messages directly to mobile devices with open rates consistently above email, but success hinges on list quality, compliance with CASL and TCPA, timing, segmentation, and integration with broader digital campaigns. This guide equips decision-makers with the frameworks to deploy SMS strategically rather than tactically.
SMS bypasses inbox filters, notification settings, and app-install friction. A text arrives on the lock screen whether the recipient uses Gmail, Outlook, or no email client at all. This universality makes SMS the channel of last resort for time-sensitive promotions, appointment reminders, and transactional updates like shipping confirmations. The tradeoff is character limits—160 characters for standard messages, 306 for Unicode—and zero room for visual hierarchy. Every word must earn its space. SMS also lacks native analytics beyond delivery and click-through on shortened links; attribution requires UTM discipline and integration with your analytics stack. Decision-makers should view SMS as a precision instrument for high-intent moments, not a replacement for nurture sequences or educational content that email handles better. The medium's strength is immediacy and ubiquity; its weakness is brevity and the user's low tolerance for irrelevance.
In Canada, CASL mandates express opt-in before you send commercial electronic messages. Pre-checked boxes, implied consent from a business relationship, or passive list imports do not suffice. You need affirmative action—a checkbox the user ticks, a keyword they text to a short code, or a double opt-in flow. Record timestamps and consent language; the CRTC can audit. In the US, TCPA requires prior express written consent for marketing texts, clear identification of the sender, and an opt-out mechanism in every message. State laws like California's CPRA add layers. Internationally, GDPR in the EU treats SMS as personal data processing; consent must be freely given, specific, and revocable. Violating these rules carries per-message fines that scale brutally. Compliance is not a legal-team afterthought; it shapes platform selection, list-acquisition strategy, and onboarding flows. If your consent mechanism is ambiguous, pause the program until it is airtight.
Most marketers start with aggregator platforms—Twilio, Klaviyo SMS, Attentive, Postscript—that abstract carrier complexity and offer campaign builders, segmentation, and analytics. Aggregators route messages through multiple carriers, handle opt-out lists, and provide webhooks for integration. The downside is per-message pricing that rises with volume and limited control over delivery routes. For high-volume senders or brands with deliverability concerns, direct carrier agreements or dedicated short codes offer better throughput and sender reputation. Short codes are five- or six-digit numbers shared or exclusive; toll-free numbers work for lower-volume sends and two-way conversations. API-first platforms like Twilio or Vonage suit engineering teams building custom workflows; no-code tools like SMSBump or Postscript suit e-commerce operators who want Shopify or WooCommerce plug-ins. Evaluate based on monthly send volume, need for two-way messaging, CRM integration depth, and whether you require MMS for images or richer media.
Broadcast blasts to your entire list generate unsubscribes faster than revenue. Effective SMS programs segment by behavioral signals—cart abandonment, browse activity, purchase recency, loyalty tier—and trigger sends based on event streams. A user who abandons a cart gets a reminder within two hours; a VIP customer who has not purchased in 90 days receives a win-back offer; a new subscriber gets a welcome series spread over a week. Layering geographic and temporal data prevents sending a Toronto audience a flash sale at 3 a.m. or a Vancouver cohort an Ontario-only promotion. CRM integration is non-negotiable; SMS platforms that do not ingest customer lifetime value, purchase history, or engagement scores cannot segment meaningfully. The goal is relevance tight enough that recipients expect your messages rather than tolerate them. This requires tagging every action—opens, clicks, purchases, support tickets—and feeding that data back into your segmentation engine in near real time.
SMS fatigue sets in faster than email fatigue because texts interrupt. A single irrelevant message can trigger an opt-out; three in a week almost guarantees it. Establish frequency caps by segment: transactional messages are exempt, but promotional sends should rarely exceed two per week for most audiences. Time sends to align with recipient time zones and known engagement windows—late morning or early evening typically outperform midday or late night. Avoid Sundays unless your product category has proven weekend demand. Use A/B tests on send time in small cohorts before scaling. For flash sales or limited inventory, urgency justifies higher frequency, but only if scarcity is real and the offer is compelling. Monitor unsubscribe rate by campaign; a spike above baseline indicates poor targeting or excessive volume. Adjust immediately. Unlike email, where users passively ignore messages, SMS users actively punish senders who waste their attention.
SMS performs best when orchestrated with other channels, not operated in isolation. A user who abandons a cart might receive an email within 30 minutes and an SMS two hours later if the email goes unopened. A paid social retargeting campaign can drive users to a landing page with an SMS opt-in offer for an exclusive discount. On-site personalization tools can surface an SMS signup form to high-intent visitors based on scroll depth or time on page. The key is cross-channel suppression and unified customer profiles. If someone converts via email, suppress the SMS follow-up. If they opt out of SMS, remove them from SMS-specific retargeting audiences. Platforms like Klaviyo, Omnisend, or HubSpot centralize these workflows; headless setups require custom webhooks and CDP integration. Track incremental lift by holding out control groups and measuring conversion rates for multi-channel cohorts versus single-channel. SMS rarely wins in isolation; its value emerges in the sequence.
SMS analytics start with delivery rate, open proxies via link clicks, and conversion tracking through UTM-tagged URLs. Most platforms report click-to-conversion, but this overstates SMS impact if users would have converted anyway. Incrementality testing—holding out a random segment and comparing purchase rates—isolates the true lift SMS generates. Run these tests quarterly to validate that your program drives marginal revenue, not just claims credit for existing intent. Track cost per acquisition by campaign and compare against email, paid search, and paid social. SMS often has higher CPA than email due to per-message costs, but shorter sales cycles and higher urgency can justify the premium for time-sensitive offers. Revenue per message and subscriber lifetime value matter more than vanity metrics like list size or send volume. A lean, engaged list outperforms a bloated one. Audit opt-out rates, spam complaint rates, and deliverability scores monthly; degradation in any signals either content fatigue or compliance drift.
Short codes are five- or six-digit numbers designed for high-volume messaging and often shared across multiple brands, though dedicated codes are available. They support higher throughput and are optimized for one-way promotional sends. Toll-free numbers, like 1-800 variants, allow two-way conversations and suit lower-volume use cases like customer service or appointment reminders. Short codes carry higher setup and monthly costs but better deliverability for mass campaigns; toll-free numbers are cheaper and more flexible for conversational flows.
CASL requires express opt-in before sending commercial electronic messages, including SMS. Pre-checked boxes, inferred consent, or purchased lists do not meet the standard. You need affirmative action—an unchecked box the user ticks, a keyword texted to a short code, or a double opt-in confirmation. You must also retain records of when and how consent was obtained, as the CRTC can audit. Implied consent from an existing business relationship has time limits and does not apply broadly. Violating CASL carries fines up to ten million dollars, so consent hygiene is not optional.
Most brands find that two promotional messages per week is the upper limit for general audiences before unsubscribe rates spike. VIP segments or highly engaged users may tolerate three, especially if messages are personalized and time-sensitive. Transactional messages like shipping updates or appointment confirmations do not count toward this cap. Monitor unsubscribe rate by campaign; a rate above two percent signals over-sending or poor targeting. Time-sensitive flash sales can justify higher frequency, but only if scarcity is genuine and the offer is strong enough to justify the interruption.
SMS works best as a secondary or urgency layer after email. A typical flow: send an email within 30 minutes of cart abandonment, then follow with an SMS two hours later if the email was not opened. Use cross-channel suppression so users who convert via email do not receive redundant SMS. Segment based on engagement; highly responsive email users may not need SMS, while low-open-rate cohorts benefit from the directness of text. Centralized platforms like Klaviyo or Omnisend automate these sequences; custom setups require webhooks and shared customer IDs to prevent overlap and maintain a unified experience.
Incrementality testing is the gold standard. Hold out a random control group from SMS sends and compare their conversion rate to the treated group. If the lift is statistically significant, SMS drives incremental revenue. Also track revenue per message, cost per acquisition, and subscriber lifetime value segmented by acquisition channel. High click-to-conversion rates can be misleading if the audience would have purchased anyway. Audit post-click time to conversion; if most conversions happen within minutes, SMS likely accelerated intent. If conversions occur days later, attribution may be overstated.
Postscript and SMSBump are built specifically for Shopify, offering native integrations for cart abandonment, post-purchase flows, and product recommendations via SMS. Klaviyo SMS works across Shopify and WooCommerce with deeper email-SMS orchestration and unified customer profiles. Attentive provides enterprise-grade segmentation and two-way messaging but at a higher price point. For WooCommerce, Twilio via plugins or Klaviyo are common choices. Evaluate based on your email platform, desired automation complexity, and whether you need MMS or two-way conversational features. Free tiers or trial periods let you test deliverability and workflow fit before committing.