The Question Everyone's Asking
WhatsApp has 2.7 billion monthly active users. It's the dominant messaging app in most of Europe, Latin America, and South Asia. So the question "should we use WhatsApp instead of SMS for business?" is completely reasonable.
Here's the thing though: it's the wrong question. SMS and WhatsApp aren't really competing for the same job. Understanding where each excels — and where it fails — is far more useful than picking a winner.
That said, we'll give you a direct answer at the end: for certain use cases, one clearly beats the other.
The Fundamentals
SMS
- •Works on every mobile phone ever made (no app required, no smartphone required)
- •No opt-in to a platform — just a phone number
- •Globally standardised — same technology from a Nokia 3310 to an iPhone 16
- •160 characters per segment (or 153 for multi-part)
- •No read receipts by default
- •No rich media natively (images via MMS, not SMS)
- •Universal reach: 7+ billion addressable devices
WhatsApp Business
- •Requires the recipient to have WhatsApp installed (about 55–60% of UK smartphones)
- •Rich media: images, videos, PDFs, interactive buttons
- •2-way conversation interface users are comfortable with
- •Template messages for outbound business communications (subject to WhatsApp approval)
- •Read receipts — you know when messages are seen
- •24-hour conversation windows (after that, you must use a template)
- •Pricing per conversation, not per message
Open Rates: The Nuance
You'll see a lot of articles claiming "WhatsApp has 98% open rates, same as SMS!" This is technically true but misleading.
Both channels see very high open rates — in the 90–98% range — because messages arrive as push notifications that people look at. The difference is intent and context.
WhatsApp notifications look like messages from friends, colleagues, and family. When a business appears in that same inbox, recipients often engage because the context feels personal. But as WhatsApp business messaging scales, we're seeing attention declining in certain markets — because businesses have figured out what we're discussing here.
SMS, on the other hand, is slightly more "formal" in most users' minds. A text from an unknown number gets attention precisely because it's less common than a WhatsApp ping.
The short answer? Both are high-attention channels. Open rates alone won't tell you which is right for your campaign.
Cost Comparison
This is where things get genuinely interesting.
SMS Costs
Straightforward: you pay per segment. At BulkSMSRates, UK SMS is £0.0300/segment. International rates vary — check the rates page. No monthly fees. No platform costs.
WhatsApp Business API Costs
More complex. Meta charges per "conversation" (a 24-hour window), not per message. There are two conversation types:
Utility conversations (transactional: order confirmations, OTPs, shipping updates): ~£0.0250–0.0350 per conversation.
Marketing conversations (promotional messages you initiate): ~£0.0500–0.0750 per conversation in the UK.
Plus you need a WhatsApp Business Solution Provider (BSP) to access the API. BSPs like Twilio, MessageBird, and Vonage add their own markup on top of Meta's rates — typically another 20–50%.
For a simple 1-message promotional send, WhatsApp marketing often costs 2–3x what SMS costs per recipient. For a 3-message customer service conversation, WhatsApp is genuinely cheaper than 3 SMS.
The maths depends entirely on your use case.
Reach: The Honest Reality
WhatsApp penetration in the UK is around 58–62% of smartphone users. That sounds high, but it means roughly 40% of your list won't receive your WhatsApp message at all.
SMS reaches 100% of mobile phone subscribers. No app required. No data connection required (SMS works on any cellular signal). A number you have on file will receive an SMS even if the handset is a 10-year-old basic phone.
For campaigns where reach matters — appointment reminders to older demographics, emergency alerts, broad consumer promotions — SMS wins outright.
For younger, smartphone-native audiences in high-WhatsApp markets (UK under-35s, most of India and Brazil), WhatsApp reach is close to 100%.
Compliance and Consent
SMS Compliance
Under PECR in the UK, you need explicit opt-in consent for marketing SMS. GDPR applies to the personal data (the phone number). The rules are well-established and understood.
WhatsApp Business Compliance
This is more complicated. Meta requires its own opt-in process — you can't just message people because you have their number. Recipients must opt in to receive WhatsApp Business messages. Meta's terms require a "clear opt-in" that explicitly mentions WhatsApp.
Additionally, all outbound business messages must use pre-approved message templates. These templates are reviewed by Meta before you can send them. The review takes 2–72 hours and rejections happen.
This means less flexibility than SMS for testing message variants or sending spontaneous campaigns.
Two-Way Messaging
Here's where WhatsApp genuinely wins.
SMS two-way messaging exists (using virtual numbers or shortcodes), but the experience is clunky. There's no threading, no media, no "read" UI.
WhatsApp is a conversation platform. If you want customers to reply with their order number, confirm an appointment, ask a question, or interact with your business in a natural way — WhatsApp is simply better. The UX is familiar, replies happen instantly, and you can send images, voice notes, or documents in response.
For customer service and support use cases, WhatsApp wins clearly.
Template Restrictions vs Creative Freedom
Marketing on WhatsApp requires approved templates. You can't just type out "30% off today only, shop now!" and send it. You need to create a template, submit it to Meta, wait for approval, and only then send.
This process works fine for regular campaigns with predictable messages. It's genuinely limiting for reactive marketing — a flash deal that needs to go out in the next hour, or a message reacting to a news event.
SMS has no template approval process. Write a message, send it. This creative flexibility is underrated.
The Verdict: When to Use Each
Choose SMS when:
- •You need guaranteed reach across all devices and demographics
- •Speed matters — no approval process, send immediately
- •Budget is a primary constraint (SMS is cheaper for single-touch sends)
- •Your audience includes non-smartphone users or older demographics
- •You're sending internationally to markets with variable WhatsApp penetration
- •Compliance simplicity matters
Choose WhatsApp when:
- •Your audience is smartphone-native and heavily uses WhatsApp (UK under-35s, India, Brazil, Latin America)
- •You want rich media: product images, PDFs, interactive buttons
- •Two-way conversation is important to the use case
- •You're running customer support or post-purchase follow-up flows
- •You have time to get templates approved
Use both when:
- •You're a sophisticated operation that can manage two channels
- •You want to try WhatsApp first and fall back to SMS for non-deliveries
- •Different customer segments have different channel preferences
The Hybrid Approach in Practice
Some of our larger clients run exactly this: they attempt WhatsApp delivery first for any number where they have WhatsApp opt-in data, and automatically fall back to SMS if the WhatsApp message isn't delivered within 60 seconds.
This gets them WhatsApp's rich media experience for the segment that wants it, and the guaranteed reach of SMS for everyone else.
Setting this up requires a bit of engineering, but the BulkSMSRates API handles the SMS fallback side reliably.
The Bottom Line
WhatsApp is a genuinely useful channel for business messaging. It's not a replacement for SMS. They're complements, not competitors.
If you're only going to run one channel right now: SMS is lower friction, cheaper to start, requires less infrastructure, has simpler compliance requirements, and reaches everyone on your list. Start with SMS, add WhatsApp when you have the operational bandwidth to manage both properly.