Ecommerce SMS Marketing: Opt-In, Setup and ROI

SMS remains the most direct lifecycle marketing channel. A text message, read within minutes, with no news feed algorithm and no Promotions tab. For an ecommerce brand, it's an owned revenue lever that complements email on high-intent moments: product launches, cart abandonment, restocks, flash sales.

But SMS doesn't launch the way an email campaign does. Consent is stricter, the regulatory constraints are heavier, and the cost per message is higher. Executed poorly, the channel burns margin and customer trust. Executed well, it generates a disproportionate ROI relative to the volume sent.

This guide covers the three pillars of a profitable ecommerce SMS program: compliant opt-in collection, technical setup on Klaviyo and Brevo, and a method for steering the channel's real ROI.

Why SMS works in ecommerce

SMS is not a volume channel. It's a precision channel. Its effectiveness rests on three properties email no longer has:

• Near-immediate read rate. A text is read within minutes of arriving, with no competition from 40 other messages sitting in an inbox.
• A strong intent signal. Giving up a phone number is a more committing act than giving an email address. The SMS list is smaller, but more qualified.
• Complementarity with email. SMS follows up where email fails (non-openers, short windows like a flash sale) and reinforces existing flows without cannibalizing them.

According to data published by Klaviyo, 72% of consumers say they made a purchase after receiving a branded text, and more than 50% say they made 2 to 3 purchases. These figures come from the vendor's marketing page (the primary source is not specified).

Benchmarks from the top 10% of Klaviyo accounts confirm the channel's potential on two key verticals:

Source: Klaviyo SMS Marketing

These benchmarks cover the top 10%. Average performance will be lower, but the order of magnitude shows the channel generates measurable revenue from the first sends.

SMS opt-in: the rules to follow in France

This is the starting point, and the most frequent blocker. SMS regulation in France is stricter than for email. Here is what applies.

Prior consent is mandatory

The CNIL requires prior consent (opt-in) for any commercial SMS to individuals. Pre-checked boxes are banned. One important clarification: accepting a merchant's terms of sale does not amount to consent to be solicited commercially by text.

Existing-customer exception (to be scoped carefully)

An exception exists for customers who have already bought: SMS prospecting without prior consent is possible, but only for products or services similar to those already purchased. The CNIL specifies that this exception cannot be used where no actual sale has taken place.

In practice, it's better not to rely on this exception as a primary strategy. Explicit opt-in protects the brand and improves list quality.

Consent separate from email

Klaviyo requires that SMS consent be collected separately from any other marketing channel. A single "Sign me up for the newsletter and texts" checkbox is not enough. Two distinct actions are required.

Quiet hours

In France, SMS quiet hours ban sending before 8am, after 10pm, on all Sundays, and on public holidays. French carriers block messages outside those windows: the message simply won't be delivered.

For brands that also sell into the United States, the framework differs: TCPA quiet hours ban sending before 8am and after 9pm, and some states such as Florida restrict the window to 8am to 8pm.

Penalties

GDPR penalties for SMS non-compliance can be severe. This isn't theoretical: the CNIL has already sanctioned companies over non-compliant SMS campaigns.

To go deeper on the GDPR framework applied to SMS, see our dedicated article: SMS and GDPR in France.

Collecting SMS opt-in: 5 methods that work

List size directly drives the channel's ROI. Here are the most effective collection mechanisms in ecommerce.

1. Dedicated pop-up or multi-step form

A classic email signup form can build in a second step for SMS collection. The principle: step 1 collects the email, step 2 offers SMS opt-in with a dedicated incentive (early access, SMS-only exclusive offer). Consent stays separate, each channel gets its own agreement.

For pop-up best practices, see Email pop-up and signup form strategy.

2. Checkout opt-in

Klaviyo supports collecting SMS consent at checkout on five platforms: Shopify, Magento 2, BigCommerce, WooCommerce and PrestaShop. This is the capture point with the best conversion rate, because the customer is already in a buying context and their phone number is already on the form.

3. Post-purchase in the confirmation flow

The post-purchase flow is a good moment to offer SMS opt-in. The customer just ordered, trust is at its peak. A message like "Get your delivery updates and exclusive offers by text" converts better than a cold pop-up.

4. SMS-only landing page

For product launches or private sales, a dedicated landing page with a pure SMS form (no email) creates a sense of exclusivity. Conversion volume is lower, but subscriber quality is higher.

5. SMS keyword opt-in

"Text JOIN to 12345" works well offline (packaging, card inserts, events) and on social media. Klaviyo supports this mechanism for brands with a dedicated number.

Double opt-in: when to turn it on

Klaviyo requires double opt-in for abandoned-cart SMS flows in the United States. Beyond that requirement, double opt-in is particularly recommended in Germany and certain EU countries.

In France, double opt-in isn't legally required (explicit single opt-in satisfies the CNIL), but it strengthens proof of consent. For a brand selling into several European countries, turning it on by default simplifies compliance.

Technical setup: Klaviyo and Brevo

Klaviyo SMS

Klaviyo is the most widely used platform for SMS in DTC ecommerce. Here are the key setup points:

• Usage-based pricing. Every text sent is billed by Klaviyo, with no separate subscription tied to the channel. That's enough to test the channel on a small volume before scaling up.
• All-in pricing. Klaviyo bundles carrier fees into the displayed rate: no hidden surcharge. The exact rate per text varies by country and number type (the detailed grid is available in the account).
• SMS segmentation. A standard text is limited to 160 characters per segment, or 70 with emoji. Longer messages are split into segments billed individually. A 200-character text costs the price of two segments.
• Sender identification. Every text sent in the EU must identify the sender, and keeping proof of consent is mandatory.

For the full setup guide, see Klaviyo SMS: setup, consent and ecommerce flows.

Brevo SMS

Brevo takes a different approach: SMS on a pay-as-you-go basis, starting at $0.0109 per credit in the United States, with no monthly minimum, no contract and no credit expiration. Pricing for other countries isn't published on the public pricing page: you need to check your account or contact support.

The Brevo model suits brands that send irregular volumes (one-off campaigns, seasonal spikes) and don't want to commit to a monthly plan.

For the full setup, see Brevo 2026 tutorial: complete setup in 11 steps.

Customer.io (SaaS)

For SaaS companies using Customer.io, the model is credit-based: 1 SMS segment equals 160 characters, and 1 MMS consumes 3 credits. MMS is limited to the United States and Canada. The detail is in our article Customer.io for SaaS.

Steering SMS ROI

SMS ROI is measured differently from email. The cost per message is higher, the list is smaller, and attribution has to be tight to avoid overstating impact.

Metrics to track

For a full dashboard, see CRM KPIs: the 12 lifecycle metrics to track.

Three principles for a positive ROI

Send little, send well. SMS is not a weekly newsletter channel. Brands that perform well send 4 to 8 SMS campaigns a month, targeted at precise segments (VIPs, recent buyers, email non-openers). Beyond that, the opt-out rate climbs and ROI collapses.

Reserve SMS for high-conversion moments. Automated flows (cart abandonment, back-in-stock, post-purchase) generate a higher RPR than broadcast campaigns. SMS in a flow costs less per dollar of revenue generated, because it reaches contacts at the right moment.

Measure the incremental, not just the attributed. A text sent to a customer who would have bought anyway didn't generate incremental revenue. To isolate the real impact, test with control groups (holdout groups): 10% of the list doesn't receive the text, and you compare conversion rates. It's the only reliable method. We cover this logic in Multi-touch email attribution.

Mistakes that wreck SMS ROI

• No segmentation. Sending the same text to the whole list multiplies cost and fatigues the least engaged contacts. Klaviyo segmentation applies to SMS exactly as it does to email.
• Messages that are too long. A 320-character text costs the price of two segments. Every word has to earn its cost. No pleasantries, no unnecessary disclaimer: one message, one CTA, one link.
• Ignoring quiet hours. A text sent outside the window in France won't be delivered. That's budget thrown away. Check that your platform handles time zones automatically.
• No link between email and SMS. SMS doesn't replace email. The two channels need to be orchestrated together, with priority rules and delays between touchpoints. See Klaviyo omnichannel marketing: orchestrating email, SMS and push.

FAQ

Do I need a separate opt-in for SMS and email?

Yes. Klaviyo requires that SMS consent be collected separately from any other marketing channel. That's also the CNIL's position: a single blanket consent isn't enough.

How much does SMS marketing cost on Klaviyo?

The rate varies by country and number type, billed per message segment sent. Klaviyo bundles carrier fees into the displayed price (no hidden surcharge). The detailed pricing grid is available in your Klaviyo account.

Can we send texts on Sundays in France?

No. French quiet hours ban any commercial text on Sundays, on public holidays, before 8am and after 10pm. Carriers block messages outside those windows.

What ROI should I expect from ecommerce SMS?

ROI depends on volume, segmentation and send type (flow versus campaign). Klaviyo's top 10% benchmarks show revenue per recipient between $0.80 and $0.85 depending on the vertical. The important part is measuring the incremental with control groups, not just attributed revenue.

SMS or email: which one should we choose?

Both. SMS doesn't replace email: it complements it on short-window moments (flash sales, restocks, cart follow-ups). Email remains the volume and content channel. The real question is orchestration between the two, not an exclusive choice.

Want your SMS opt-in flow and ROI tracking reviewed? Talk to the Deliver team.