Texts cost money, carry legal risk and earn on the clock. Send only on the clock.
Your per-recipient math is missing a cost line. One more email costs you close to nothing. Every text is billed per message, and a picture message costs more. Texts also run under consent rules stricter than email's. Together, those make SMS worth sending only when the timing does the selling.
Get prior express written consent before you send a marketing text. Put the disclosure beside the phone field: the customer agrees to receive recurring automated marketing texts at that number, consent isn't a condition of purchase, how often you'll text, that message and data rates may apply, and how to get help or stop.
A phone field without that disclosure collects numbers, not permission. Add a keyword confirmation as good practice: the customer replies YES before the first marketing text. It proves the person who typed the number holds the phone, so a typo doesn't put a stranger on your list. Register your number type with the carriers before the first send; your SMS platform will walk you through it.
Federal rules bar telemarketing before 8am or after 9pm in the recipient's local time, and texts count. Florida is stricter, at 8am to 8pm, and Florida, Oklahoma, Maryland and Oregon cap marketing texts at three per person per 24 hours. Send on the recipient's clock, and cap to the strictest state you text into.
Your SMS platform probably enforces quiet hours for campaigns. Check that your flows and any API sends do too. A flow fires when its trigger fires, so a cart abandoned at 11pm, the customer's time, can get a text within the hour. Unless something holds it, that text breaks the federal window. A custom integration that posts to the API needs the same check.
Honor a STOP, or any other reasonable way of saying it, right away. The federal outer limit is ten business days, and one confirmation text with no marketing in it is allowed. Treat a STOP as a stop for all your marketing texts. Before you text a list that has been quiet for a year, run it through the FCC's Reassigned Numbers Database.
Test your own opt-out path. Reply "cancel" and "unsubscribe" from your phone, and confirm both remove you.
Carriers reassign numbers, so a list that sat unused for a year holds some that now belong to someone else. A number that changed hands is a stranger who never agreed to hear from you. The consent you recorded belongs to the old owner, which is why the check comes before the send.
Add the cost line to every SMS forecast. For example, at an assumed one cent a text, a send to 20,000 subscribers costs $200 before anyone clicks. It has to earn more than a cent per recipient to cover itself on revenue. A picture message raises that bar. Email carries no such line, which is why the same offer can pay by email and lose money by text.
Opt-out rate per send is the SMS complaint rate. Put it on The Monday Scorecard beside spam rate. An SMS list can't be re-permissioned cheaply. Once someone texts STOP, the only way back is a fresh opt-in they choose to give. Smart Sending skips anyone you texted in the last 24 hours by default, so reconcile text campaigns the way you reconcile email.
Send texts where the timing does the selling: replenishment timed to the interval, delivery, abandonment. Each has a reason to arrive today: the bottle is nearly empty, the box is at the door, the cart is still open. Campaign blasts burn the list, because a text with no reason to arrive today reads as noise.
Cap SMS on its own, apart from email. Start at two texts per person per week, counting campaigns and flows together. Lower the cap when opt-out rate per send rises. Never email and text the same person on the same day for the same message.
Capture in two steps: email first, then phone, each step with its own consent. The email step converts on its own, so a visitor who won't share a number still joins. The phone step then asks people who have already said yes once, with its disclosure beside the field.
If SMS runs in a different platform from email, your holdout segment, cadence caps and sale suppressions don't exist for SMS until you mirror them there. A customer held out of email who still gets texts spoils the holdout read. A customer capped at two emails can still get four texts the same week.
The abandonment email is off, and nobody knows. It starts as a deliberate pause: someone turns the email off to fix a rendering problem, then leaves the company. The SMS branch keeps sending, recovery revenue keeps arriving under the SMS line, and the monthly total looks healthy. I've found it dark for more than a year. Open your abandonment flow today and confirm the email branch is live.
[Brand]: your [product] should be running low about now. Reorder the same one in one tap: [link]
Reply STOP to opt out.
This is one chapter of The Second Order, which is free and readable in full on a single page with no form in front of it.