One is nearly free. The other costs per send.
That single difference drives every other decision: what you send, how often, and how quickly you can burn a list you spent a year building.
Our bias, declared
Most brands should build email first and add SMS for a narrow set of time-sensitive moments. SMS produces higher engagement rates that make it look better in a dashboard, but it carries a per-message cost, a far harsher consent regime, and a list that punishes overuse permanently. Email's economics forgive experimentation; SMS's do not, and treating SMS as a second broadcast channel is the most common way we see brands destroy an expensive asset.
Side by side
| Factor | SMS | |
|---|---|---|
| Cost per message | Effectively zero at volume | Real per-segment cost, every send |
| Open / read rate | 20–40% typical | Read almost immediately |
| Speed of response | Hours to days | Minutes |
| Consent requirements | Straightforward opt-in | Express written consent, tightly regulated |
| Legal exposure if you get it wrong | Deliverability damage | Statutory damages per message |
| Room for content | Unlimited, designed | A sentence and a link |
| Tolerance for frequency | Several a week if segmented | Two to four a month before churn |
| Cost of a mistake | Send an apology | You paid to annoy everyone |
| Suitability for urgency | Poor, competes with a full inbox | Excellent |
| Revenue per subscriber per year | Higher in absolute terms | Higher per message, smaller list |
Choose email when
The message needs more than a sentence
Education, storytelling, product explanation, anything with more than one link. SMS forces you to compress everything to a line and a URL, which works for a reminder and fails for an argument.
You want to experiment
Zero marginal cost means you can test subject lines, segments and cadence without spending anything but attention. Every SMS test costs money per recipient, which is why SMS programs tend to ossify around whatever worked once.
Your list is large and your margins are thin
At a hundred thousand subscribers, a per-message cost turns a broadcast into a meaningful line item. Email's economics scale with your list; SMS's economics work against it.
You need an owned asset that compounds
An email list is portable, exportable and outlives any platform. It remains the most durable owned audience available, which is why it survives every prediction of its death.
Choose sms when
The moment is truly time-sensitive
Back in stock on a product they asked about, an order out for delivery, a flash window closing tonight, an abandoned cart within the hour. SMS earns its cost when the value of arriving now is real, and only then.
Your customer isn't an inbox person
Some audiences (younger, mobile-first or in categories where nobody reads promotional email) simply don't open. If email engagement is structurally weak after you have fixed deliverability and segmentation, SMS may be where your audience actually is.
The transaction is high-frequency and low-consideration
Food, convenience, ride-hailing, anything repurchased weekly. The message is short by nature and the decision window is minutes, which is exactly SMS's shape.
You need a channel email can't reach
When deliverability has collapsed and rebuilding sender reputation will take months, SMS reaches customers who are no longer seeing your email at all. Treat it as a bridge, not a replacement.
The economics people get wrong
SMS dashboards report engagement rates that make email look broken: read rates near total, click rates several times higher. The comparison is misleading because the lists aren't comparable. An SMS list is smaller, more recently opted in, and self-selected for people who wanted messages badly enough to hand over a phone number. Compare revenue per subscriber per year, not rate per send, and the gap narrows sharply.
Then add the cost side. Each segment of each message costs money, and a message over the character limit silently becomes two. A monthly program to fifty thousand subscribers is a real recurring expense that email at the same list size effectively is not. Model it as cost per incremental order, not cost per send.
The consent rules are where the real risk is. SMS marketing in the US requires express written consent with specific disclosure, and statutory damages apply per message. A badly built list isn't a deliverability problem. It's a lawsuit problem. Buying or inferring phone numbers is the fastest way to turn a growth channel into a legal one, and no engagement rate justifies it.
Related questions
Two to four messages a month for most consumer brands, and treat every one as spending down a balance. Opt-outs on SMS are permanent and immediate in a way email unsubscribes aren't. People leave a text list faster and never come back. If your calendar has weekly SMS on it, you're converting a durable asset into one quarter's revenue.
Other comparisons
Services referenced
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