Most ecommerce SMS programs are priced like everyone on the list is worth the same. They aren't. If you pull up your revenue-by-customer report and sort it, you'll usually find a small cluster of repeat buyers — call it the top 5% — that produces a wildly disproportionate share of the money. In a lot of stores that slice drives something like 40% of SMS-attributed revenue. Round numbers, but the shape is real.
Full disclosure: I work for ReadySMS, so I have a horse in the "send more SMS" race. That's exactly why I want to do the math honestly here — because the honest version says send more to some people and less to others, which is not the same as "blast everyone more."
The trap: measuring cost per send instead of cost per dollar
When you look at an SMS bill, the natural instinct is to minimize cost per send. Fewer segments, cheaper tier, done. But that's the wrong denominator. What you actually care about is cost per dollar earned — how many cents of send cost it takes to produce a dollar of revenue.
Those two numbers point in opposite directions once you segment. A blast to your whole list has a low cost per message but a mediocre cost per dollar, because a big chunk of the list barely converts. A targeted send to VIPs costs the same per message but earns multiples more per message sent.
Let me build the example.
Setting up the model
Say you have a 40,000-contact opted-in SMS list. That volume puts you on ReadySMS's Starter tier at $0.0155/segment, plus the flat $0.0045/segment carrier pass-through, so your all-in cost is $0.0200 per segment. (Tiers and the pass-through are laid out on the pricing page.)
Your message is a 150-character promo — GSM-7, no emoji — so it fits in a single 160-character segment. One segment per recipient. Clean.
Now split the list:
- VIP segment (top 5%): 2,000 contacts. These are repeat buyers, high AOV, high engagement.
- The rest (95%): 38,000 contacts. Occasional buyers and dormant subscribers.
I'll use round, clearly-approximate conversion assumptions — treat them as illustrative, not gospel:
| Segment | Contacts | Conv. rate | Avg. order | Revenue |
|---|---|---|---|---|
| VIP (top 5%) | 2,000 | 8% | $90 | $14,400 |
| The rest | 38,000 | 1.2% | $55 | $25,080 |
| Full list | 40,000 | — | — | $39,480 |
So a single full-list blast earns ~$39,480. The VIPs, at 5% of the list, produce ~36% of that revenue — close enough to the "40%" headline. Now watch what the cost side does.
The cost-per-dollar math on one blast
Every contact gets one segment at $0.0200.
Full-list blast:
- Send cost: 40,000 × $0.0200 = $800.00
- Revenue: $39,480
- Cost per dollar earned: $800 / $39,480 = $0.0203 (about 2 cents to earn a dollar)
Great ratio. SMS is cheap; this is why the channel works. But break it apart by who you were actually paying to reach:
VIP portion only:
- Send cost: 2,000 × $0.0200 = $40.00
- Revenue: $14,400
- Cost per dollar earned: $40 / $14,400 = $0.00278 (0.28 cents)
The-rest portion only:
- Send cost: 38,000 × $0.0200 = $760.00
- Revenue: $25,080
- Cost per dollar earned: $760 / $25,080 = $0.0303 (3.0 cents)
The VIP send is roughly 11x more cost-efficient per dollar than the send to everyone else. Same message, same per-segment price. The only variable is who's on the receiving end.
What this means for send frequency
Here's the part people miss. If your VIP send returns a dollar for 0.28 cents of cost, you have enormous room to send them more often before the math turns ugly.
Say you currently send both groups 4 campaigns a month. Consider a plan where VIPs get 8 and everyone else stays at 4 (or drops to 3 to protect opt-in health — more on that in a second).
Monthly cost under the flat plan (4 each):
- VIP: 2,000 × 4 × $0.0200 = $160.00
- Rest: 38,000 × 4 × $0.0200 = $3,040.00
- Total: $3,200.00
Monthly cost under the concentrated plan (8 VIP / 3 rest):
- VIP: 2,000 × 8 × $0.0200 = $320.00
- Rest: 38,000 × 3 × $0.0200 = $2,280.00
- Total: $2,600.00
You doubled VIP frequency and your total send bill went down ~$600, because you trimmed one low-yield blast to the 95%. The extra four VIP sends cost $160/month. If each of those four sends performs anywhere near the 0.28-cents-per-dollar VIP ratio, that $160 is buying multiples of itself in revenue.
That's the whole argument: frequency should follow cost-per-dollar, not headcount.
The frequency ceiling is real — respect it
Doubling VIP sends only works if you don't fatigue them into unsubscribing. A VIP who opts out isn't a lost send; it's a lost lifetime value stream, which is far more expensive than any segment fee.
A few guardrails I'd put on this:
- Cap VIP frequency by behavior, not a fixed number. Someone who bought last week can hear from you more than someone who bought four months ago.
- Watch opt-out rate as your governor. If VIP unsubscribes tick up when you go from 4 to 8, back off. The conversion metrics that matter include opt-out rate for exactly this reason.
- Vary the message. Eight identical "20% off" texts a month train people to ignore you. Mix restocks, early access, post-purchase check-ins.
- Don't over-message the 95% to compensate. The temptation is to "make up" revenue by blasting the dormant group harder. That's the highest-cost-per-dollar send you have. There are ecommerce moments where SMS is the wrong channel entirely — dormant subscribers are often better re-engaged by email first.
Watch the segment count, not just the recipient count
The math above assumed a tidy single-segment message. Real promos aren't always that disciplined.
A 175-character promo with one emoji drops you into unicode territory — the limit falls to 70 characters per segment (67 for multipart) — so that message becomes 3 segments. Run that on the VIP 8-send plan:
- 2,000 × 8 × 3 × $0.0200 = $960.00/month just for VIP
Versus the single-segment version at $320.00. You tripled your VIP cost with one emoji and a couple of extra sentences. It's still cheap on a cost-per-dollar basis, but the point stands: know your segment count before you decide frequency. Trim the emoji, tighten the copy, and you keep the frequency without tripling the bill. The ReadySMS calculator will show you segment counts before you send.
Where the tier math kicks in
If your VIP program scales — more contacts, higher frequency — total volume climbs and you can cross a pricing breakpoint. At 50,000+ segments/month you move from Starter to Growth at $0.0125/segment, and the rate drops further. High-volume senders can eventually reach the Enterprise tier at $0.0028 (500K+ segments/month) plus pass-through.
That's a second-order lever, and it compounds with segmentation rather than replacing it. If you want to see how tier crossovers actually change unit economics, the agency margin-by-tier breakdown walks through the same kind of breakpoint math from the reselling side, and the enterprise tier breakeven post covers the very top end.
The practical takeaway
You don't need a data science team to act on this. The steps:
- Define your VIP segment — top 5% by revenue or by repeat-purchase count is a fine start.
- Measure cost per dollar earned separately for VIPs and everyone else. You'll almost certainly find a 5–15x gap.
- Raise VIP frequency deliberately, watching opt-out rate as your brake.
- Trim, don't multiply, sends to the low-yield 95%.
- Count your segments before committing to a frequency, especially if you use emoji or long copy.
The reason transparent per-segment pricing matters here is that it lets you do exactly this arithmetic. When your bill separates the send rate from the flat carrier pass-through, "what does one more VIP send actually cost me" is a number you can compute, not guess.
If you want to run your own version of the model, the cost calculator handles the segment and tier math, and the ecommerce ROI calculator post covers the revenue side. Start with your own top-5% list and see where your cost-per-dollar gap actually lands — it's usually wider than people expect.