Both channels put a message on a customer's phone. After that they behave very differently, and the differences decide which one fits a given job.

This compares the two on the things that actually change the decision: what each one costs per message, how long a message can be, what you can attach, what consent each one requires, and what you can tell about whether it arrived.

Everything here comes from platform documentation, regulators and published price lists. Where a widely repeated number could not be traced to a source, it is not used, and there is a section below explaining which number that is and why it matters.

When to use WhatsApp, and when to use SMS

SMS reaches any mobile phone, needs no app, and has no time limit on when you can send. That makes it well suited to one-time passcodes and to short, urgent notifications where reach matters more than richness.

WhatsApp supports much longer messages, media, documents and interactive elements, gives you delivered and read states, and is built for two-way conversation. That makes it better suited to service conversations, richer notifications and campaigns where you expect a reply.

The useful question is not which is better. It is which job you are doing. There is a table for that at the end.

About that 98% open rate

The figure appears in a great many articles about WhatsApp. It cannot be traced to a study with a published sample, fieldwork period or definition of what counts as an open.

Looking specifically for a credible independent comparison of WhatsApp and SMS deliverability or response rates, across two rounds of research, turned up nothing that meets a basic evidence standard: a named sample, a stated fieldwork period, a matched audience and a defined metric. Vendor percentages without a stated method were excluded.

That does not mean WhatsApp performs badly. It means nobody has published defensible evidence about how the two compare, and quoting a number that cannot be sourced is not a good basis for a channel decision.

What can be verified is the mechanism underneath the claim. The WhatsApp Business Platform reports message statuses of sent, delivered, read, played and failed. SMS has no standard network-level read receipt; delivery receipts exist, but a read state does not. So if measuring whether a message was actually read matters to you, that difference is real and documented, which is more than the open-rate figure offers.

What each channel costs

Two different pricing models, which is why a single comparison number is misleading.

SMS is priced per segment. Twilio's published list price is US$0.056 per outbound SMS segment to UK mobile numbers and US$0.1355 to South African numbers, with inbound at US$0.0075. Those are one provider's list prices rather than a market average, but they give an order of magnitude.

The word "segment" is doing a lot of work there. See the next section.

WhatsApp is priced per delivered message by Meta, with the rate set by message category and the recipient's country. Since 1 October 2026, service messages are charged after the first 1,000 per business phone number each calendar month, and utility templates sent inside an open 24-hour window are chargeable too. Our WhatsApp Business pricing guide covers the model in detail.

One more cost difference that is easy to miss: on WhatsApp, receiving messages from customers costs nothing and undelivered messages are not billed.

Message length, media and timing

Three practical differences that shape what you can actually send.

Length. One SMS segment holds 160 characters using the standard GSM-7 alphabet, or 70 if the message contains characters that require UCS-2, which includes most emoji and many accented characters. Longer messages are split, and concatenated segments hold 153 or 67 characters each because part of the space is used to stitch them together. So a 300-character SMS is three segments and costs three times as much, and one emoji can more than double the segment count of a message.

WhatsApp free-form text messages allow up to 4,096 characters in a single message.

Media. WhatsApp supports images, video, audio, documents, location and contacts, with published file size limits, alongside interactive elements like reply buttons and list menus. SMS is text, with MMS as a separate and less consistently supported route.

Timing. This is the biggest operational difference, and it usually gets a single line in comparisons that deserve more.

WhatsApp works on a 24-hour customer service window. When a customer messages you, a window opens, and each new message from them resets it. Inside that window you can reply freely. Once it closes, you can only reach them with a message template that Meta has approved in advance.

SMS has no equivalent. You can send whenever you like, subject to the consent rules below.

That difference cuts both ways. The window means WhatsApp campaigns need templates approved ahead of time, which takes planning. It also means WhatsApp conversations are, by design, conversations the customer started.

Identity differs too. A WhatsApp business number carries a registered display name and business profile. SMS is sent from a number, a short code or an alphanumeric sender ID, with availability varying by market.

Consent and the rules

Both channels are governed by the same principle in both of Cue's markets: you need permission, and you need to make stopping easy.

In the United Kingdom, PECR requires consent for marketing messages sent to individuals. There is a narrow soft opt-in for existing customers whose details you collected during a sale or negotiation, where you are marketing your own similar products and you offered an opt-out at collection and in every message since. The ICO treats direct messages on messaging services as covered by the same rules as texts, so WhatsApp is not a way around PECR. UK GDPR applies on top, requiring a lawful basis, transparency and respect for objection.

Worth noting: the ICO's direct marketing guidance is currently under review following the Data (Use and Access) Act 2025, so this is an area to keep an eye on.

In South Africa, POPIA section 69 prohibits unsolicited electronic direct marketing unless the person has consented or is an existing customer under similar-product conditions. A prospect who has not objected may be approached once to ask for consent. Every message has to identify the sender and provide a way to opt out.

The practical version: a list you bought is a problem on both channels. On WhatsApp it is also a quality-rating problem, because blocks and reports feed back into your ability to send at all.

Which to use, by job

On the two markets. WhatsApp usage is high in both the UK and South Africa. Ofcom's Online Nation 2025 reported that WhatsApp reached 90% of UK online adults in May 2025. Ofcom does not publish the panel size in the accessible summary, so treat it as an indicative regulator figure rather than a precise measurement. For South Africa, no equally well-sourced figure was available, though WhatsApp's position in the market is well established.

Rather than choosing one channel for everything, most teams end up using both for different jobs. The decision is per use case, not per company.

Where to start

If most of what you send is one-way and time-critical, SMS is doing a job WhatsApp cannot do better, and there is no reason to move it. If you are sending things customers reply to, or want them to reply to, that is where the two channels genuinely separate.

If that is the direction you are heading, the WhatsApp channel overview covers what running it properly involves, from templates and approval through to handling the replies.