The open rate advantage of SMS is real, but so is the compliance complexity. SMS marketing is more regulated than email in most jurisdictions, and the cost of non-compliance (fines under GDPR in the UK/EU, TCPA violations in the US) significantly exceeds the cost of getting the setup right from the start.
Compliance: what you need before sending any SMS
UK and EU (GDPR). You must have explicit opt-in consent to send marketing SMS messages. This means customers actively opting in to SMS specifically - not just to "marketing communications" generally. A pre-ticked checkbox or a phone number field with no consent explanation is not sufficient. The opt-in must be unbundled from other consents (SMS consent and email consent collected separately), documented, and revocable on request.
US (TCPA). Similar requirements plus specific rules about opt-in language, mandatory opt-out keywords (STOP, CANCEL, UNSUBSCRIBE), and required disclosure of message frequency. Violations carry per-message fines that can accumulate quickly.
All major SMS apps (Postscript, Klaviyo SMS, Attentive) provide compliant opt-in widgets, consent language templates, and automated opt-out handling. Use them - don't build your own compliance workflow.
SMS tools for Shopify
Postscript is the most widely used dedicated SMS marketing tool for Shopify. Strong US focus (best for brands with primarily US customer bases), deep Shopify integration, good automation flows, and excellent list growth tools. Pricing based on message volume.
Klaviyo SMS integrates SMS with your existing Klaviyo email account. If you're already on Klaviyo, adding SMS gives you a unified platform where email and SMS flows can be coordinated - the same customer journey orchestrated across both channels. Available in US, UK, Canada, and Australia.
Attentive is the enterprise SMS platform of choice for larger DTC brands. More expensive, more sophisticated (advanced audience segmentation, A/B testing, predictive send timing), and requires a minimum spend commitment. Appropriate for stores doing $5M+ where SMS is a primary revenue channel.
For UK-based stores with UK customers, check geographic availability before committing to a tool. Some US-centric SMS platforms have limited UK carrier support and higher costs for UK numbers.
The flows that generate SMS revenue
Abandoned cart SMS. Sent 30-60 minutes after checkout abandonment. Outperforms email on open and click rates because SMS arrives in the same inbox as personal messages. Keep it short: the product name, a direct link to the cart, and an optional incentive ("Your cart is waiting - complete your order in the next 2 hours for 10% off"). One message maximum - multiple abandon cart SMS messages cross the line from helpful to intrusive.
Back-in-stock alert. When a previously sold-out product is restocked, an SMS to customers who opted in to stock alerts generates immediate purchases. This is the highest-converting triggered SMS flow because the recipient specifically requested the notification.
Flash sale announcement. A 4-hour or 24-hour sale sent to your SMS list drives urgency that email typically doesn't. The immediacy of SMS (98% of messages are read within 3 minutes) is perfectly matched to time-limited offers. Keep the message brief: the offer, the deadline, and a link.
Post-purchase support. "Your order has shipped - track it here: [link]" is a transactional message (not marketing) but it drives satisfaction and reduces "where is my order?" support contacts. Transactional SMS doesn't require marketing consent.
Building your SMS list
You cannot send marketing SMS to customers who didn't explicitly consent. This means you need to build your SMS list separately from your email list, even if you already have thousands of email subscribers.
Effective SMS opt-in placements:
- A dedicated SMS opt-in popup (separate from your email popup, or a second step after email capture: "Also get texts for flash sales and exclusive offers")
- SMS opt-in at checkout (a checkbox below the phone number field with clear consent language)
- A keyword campaign ("Text DEALS to [number] for 15% off") promoted in your email list and social media
Your SMS list will typically be 20-30% the size of your email list - that's normal and expected. The smaller size is offset by the significantly higher engagement rate.
