WhatsApp vs SMS for business: the honest comparison.

Both channels reach essentially every mobile phone on Earth, but they don’t dominate the same markets. The cultural default in each region matters more than installed-base numbers because customers respond to channels they trust.

The cost story is more complicated than just “per message.” Both channels have multiple pricing models and the differences compound at scale.

The right way to model the cost decision is by your traffic pattern, not by the per-message comparison. One-shot transactional alerts: SMS or Business API, depending on geography. Multi-turn conversations: Mossmoon’s flat per-line model is structurally cheaper than either, where it fits.

SMS is a text channel. Hard cap of 160 characters per message (longer texts get split and reassembled, with carrier quirks). MMS exists in the US for images but is uneven elsewhere and expensive. Read receipts: no. Typing indicators: no. Voice notes: no. Documents: no. Rich link previews: depends on the recipient’s phone.

WhatsApp is a full messaging channel. Text up to 65K characters per message. Images, videos, voice notes, documents (PDFs, docx, xlsx), location pins, contact cards, link previews with full URL unfurling. Read receipts. Typing indicators. Threaded replies. Reactions. Forwarding.

For any conversation that benefits from sending a photo (real estate listings, support tickets where a customer needs to show you the broken thing, ecommerce custom-order specs), voice note, or document attachment, WhatsApp is structurally capable in ways SMS isn’t. The customer experience gap is significant.

Both channels have meaningful rules about consent and identity. The specifics differ but the underlying principle is the same: messaging people who didn’t opt in gets your sending capability shut down.

Open rate is the wrong metric for both channels because both are essentially always opened. Reply rate and time-to-reply are the real signals.

SMS reply rates for marketing or sales messages are typically below 10%. SMS skews towards one-way alerts: shipping confirmations, OTPs, appointment reminders. Customers see SMS as transactional and don’t expect a two-way conversation.

WhatsApp reply rates for similar messages are commonly 40 to 70%, often higher for warm or opted-in recipients. Customers see WhatsApp as a conversational channel and reply naturally. The same message converted from SMS to WhatsApp routinely gets multiples more engagement in markets where WhatsApp is the default.

For any business model where the value is in the back-and- forth (sales qualification, customer support, AI receptionist, coaching follow-up), WhatsApp is structurally the better channel. For one-shot transactional alerts, SMS is fine and often cheaper at scale.

Mossmoon is the WhatsApp half of this comparison via the personal API path. We’re a WhatsApp specialist; we don’t do SMS as a long-term primary channel.

If your decision lands on SMS, use Twilio, Bandwidth, MessageBird, or your country’s equivalent. We’ll point you their way without trying to talk you out of it.

If your decision lands on WhatsApp via the Business API path, use Twilio, 360dialog, WATI, or a BSP that fits your region. We have honest comparisons of those alternatives in our docs if you’re evaluating them.

If your decision lands on WhatsApp via the personal API path, you’re in the right place. Flat $15 per active line per month. First line free for 7 days. See: WhatsApp Business API vs personal WhatsApp API for the deeper comparison of the two WhatsApp paths.