Email costs you a rounding error per send. SMS costs you real money — two cents plus change every time a message lands. So the reflex among ecommerce marketers is to treat SMS as a scarce, premium channel and email as the free workhorse. That's half right. The other half is where people burn money: they build the SMS list the same way they build the email list, send it the same cadence, and then wonder why the "expensive" channel isn't pulling its weight.
Full disclosure: I work for ReadySMS, so I have a horse in the SMS race. That's exactly why I want to be honest about the parts where email quietly wins — because pretending otherwise is how you torch an opt-in list you spent months building.
The value gap is real, and it's mostly about attention
Nobody has clean, universal numbers here, so treat these as rough industry approximations, not gospel:
- Email open rates for ecommerce promos tend to land somewhere in the 15–25% range.
- SMS open rates on an opted-in list are commonly cited around 90%+, and most of those opens happen within minutes.
- Email click-through on the send often sits around 1–3%.
- SMS click-through frequently runs 10–20% for a well-targeted message.
Stack those and you get why people say an SMS subscriber is worth 3–5x an email subscriber. It's not that the medium is magic — it's that a text lands in the same thread as messages from the recipient's mom, and it doesn't get buried under 40 other promos in a Promotions tab. Attention is the whole ballgame, and SMS buys attention that email can't.
But attention you overspend is attention you lose. The 90% open rate is a loan against goodwill, not a renewable resource.
Let's put a cost on both channels
Here's a clean comparison for a 10,000-subscriber list, one send each.
| SMS (ReadySMS Standard) | ||
|---|---|---|
| Cost per message | ~$0.001 (blended ESP cost) | $0.0245 (1 segment: $0.02 + $0.0045 carrier) |
| Cost for 10,000 sends | ~$10 | $245 |
| Assumed CTR | 2% | 15% |
| Clicks | 200 | 1,500 |
| Cost per click | $0.05 | $0.163 |
SMS costs ~24x more per send. But it drove 7.5x the clicks. Per click, SMS is only ~3.3x more expensive — and every one of those clicks arrived within minutes instead of over the next two days.
Now push it to revenue. Say both channels convert clicks at 10% on a $60 average order value:
- Email: 200 clicks → 20 orders → $1,200 revenue on ~$10 spend. Cost is 0.8% of revenue.
- SMS: 1,500 clicks → 150 orders → $9,000 revenue on $245 spend. Cost is 2.7% of revenue.
SMS costs more as a percentage of revenue — and still generates 7.5x the absolute dollars off the same list size. That's the trade you're actually making: a slightly worse margin ratio for a dramatically bigger number. For most ecommerce catalogs, the bigger number wins. If you want to model your own inputs, our ecommerce SMS ROI calculator walks through the same math with your AOV and conversion rate.
The "treat them like one" trap
Here's where marketers give the value back. They take the email playbook — daily-ish promos, every product drop, every 10%-off nudge — and paste it onto SMS. On email, an over-sent list just quietly stops opening. On SMS, an over-sent list hits STOP, and that opt-out propagates permanently.
ReadySMS honors inbound STOP/UNSUBSCRIBE automatically and suppresses that contact across every future campaign. That's a compliance feature I'm glad exists — but it also means an unsubscribe is final. You don't get the email luxury of a dead subscriber who might re-open next quarter. When an SMS subscriber leaves, the 3–5x value leaves with them.
So the math changes. Every send has to clear a higher bar because the downside isn't a wasted $0.0245 — it's the lifetime value of a subscriber who churns out of annoyance. Rule of thumb I'd defend: if you wouldn't personally interrupt someone's evening to say it, don't text it.
Where SMS actually loses to email
I promised honesty. Email genuinely wins these:
- Long-form content. Newsletters, storytelling, editorial gift guides — anything past a sentence or two. A 480-character text splits into 4 segments (153 chars each after the first at 160), so a wordy promo to 10,000 people costs ~$980 instead of $245. Read the 160-vs-153 segment cliff before you write long.
- Image-heavy merchandising. A grid of six products with lifestyle shots belongs in email. MMS can carry an image but the per-message cost jumps, and there's a length where it flips — covered in SMS vs MMS cost crossover.
- Low-intent, high-frequency nurture. "Here's what's new this week" is fine in an inbox. As a text, it's a STOP magnet.
- Anything that isn't time-sensitive. If it can wait, email it. There's a whole list of these in 5 ecommerce moments where SMS loses to email.
The pattern: SMS wins on urgency and intent — abandoned carts, back-in-stock, flash windows, shipping updates, VIP early access. Email wins on volume, depth, and browse. Use each for what it's good at instead of forcing one to do both.
How to build the list so the value holds up
The 3–5x number assumes a clean, high-intent SMS list. Bolt an SMS checkbox onto a giveaway and you'll get a big list of people who don't care, and the per-message cost turns into pure waste. A few things that keep the value real:
- Ask for the phone number where intent is highest — at checkout, on a back-in-stock request, on a VIP waitlist. Not on a footer sweepstakes.
- Capture explicit consent and keep the attestation. ReadySMS records opt-in attestation on bulk and API sends, which builds the audit trail you'll want if a carrier or regulator asks. Consent strategy specifics live in crafting the perfect SMS consent strategy.
- Get your 10DLC brand and campaign registered before you scale. Unregistered A2P traffic gets carrier-filtered, so a "cheap" send that never arrives is infinitely expensive. See 10DLC compliance for ecommerce.
- Segment ruthlessly. Your top subscribers behave completely differently from the tail — your top 5% of subscribers often drive ~40% of SMS revenue. Send them more, and send the rest less.
The budget takeaway
Don't budget SMS and email as competing lines fighting over the same dollar. Budget them as two instruments with different jobs:
- Email carries reach and volume at near-zero marginal cost. It's where you tell stories, merchandise, and keep the whole list warm.
- SMS carries urgency and intent at real marginal cost — but with attention and conversion that pay for the premium several times over when you're disciplined about what earns a text.
The failure mode isn't "SMS is too expensive." It's spending SMS's higher per-message cost on messages that should've been emails, then losing subscribers to STOP and blaming the channel.
If you want to see what a disciplined SMS program costs against your own numbers, plug them into the cost calculator or skim how to actually calculate SMS ROI. ReadySMS starts with 2,500 free credits and no card, so you can model a real send before you commit a budget line to it. Send the messages that earn the interruption — and email the rest.