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Channels in depth
SMS, WhatsApp, RCS and the rest: what each is good at, the rules each comes with, and how to pick per message.
- 1Channels are not interchangeable: the most common early mistakeSMS, WhatsApp, RCS and email differ in who may start a conversation, what may be said, what silence tells you and what a mistake costs. Those differences are not cosmetic.
- Before choosing a channel, check who is allowed to start the conversation on it. WhatsApp needs an approved template; SMS needs registration and consent.
- Decide per channel what to do when nobody replies. Silence on SMS tells you nothing; on WhatsApp a read receipt does.
- Build channel rules into your sending code so a wrong send is refused with a reason, rather than discovered later from a complaint.
- 2Choosing a channel per message, not per programmeThe channel decision belongs at send time, driven by intent, region, consent and where the person actually reads — not to a procurement meeting eighteen months earlier.
- Choose the channel for each message when you send it, from its purpose, the country, your consent and the person's habits.
- Check consent again at every fallback step. Permission given for one channel never carries over to another.
- Log the reason behind every channel choice, so 'why did this go by SMS?' is answered by a lookup, not a guess.
- 3The 24-hour window: the rule that breaks most first integrationsWhy your WhatsApp test message worked and your production message did not: how the customer service window works, what it costs inside and outside, and how to design around it.
- The window opens when the customer writes and lasts 24 hours from their latest message. Outside it, only approved templates are delivered.
- Check the window at the moment of sending, not when the message is queued, and never store "can message" on the contact.
- Get the templates you will need approved before launch, and reply quickly. Since 1 October 2026 replies inside the window are charged after 1,000 free per number each month, but a quick reply still keeps you out of templates.
- 4A WhatsApp template strategy that survives contact with productionTemplates are approved in advance, billed by category and impossible to improvise. Design the set before you need it, not during an incident.
- Design about five reusable templates by purpose instead of forty one-off messages, and keep each language as its own record.
- File every template under its honest category. Meta can re-categorise mislabelled ones, and repeated rejections hurt the account.
- Get a generic incident template approved now, while nothing is wrong, so you can reach customers during an outage.
- 5What RCS changed, and what it did notApple's adoption in iOS 18 turned a long-stalled standard into something with reach, and 2026 brought new versions and cross-platform encryption. Reach is still not the same as a business case.
- Ask providers for RCS business reach in your countries, not handset support. Operator launch and business-messaging availability are the real limits.
- Design the SMS fallback first. Every RCS programme is two programmes, and part of your audience will always receive the plain version.
- Start with messages that have a next action, like delivery tracking or rescheduling. Leave one-time passcodes on SMS for now.
- 6Adding RCS to an SMS programme without running two programmesEvery RCS deployment is two deployments: the rich one and the SMS fallback. Designing the fallback first, checking capability at send time and measuring honestly keeps it from becoming a second programme.
- Write the plain SMS version of every message first; the rich version may add buttons and images, never missing meaning.
- Check RCS capability at send time, never from a stored flag, and send SMS when the answer is slow or unknown.
- Use RCS where a message replaces a task — tracking, rebooking, paying — and test it against SMS among capable users.
- 7RCS after iOS: what changed in the numbers, and what to distrustAdoption figures for RCS are widely quoted and rarely defined. What can be said confidently, and what is being counted loosely.
- iPhones have supported RCS since iOS 18, so phone support is no longer the main limit on reach.
- Real reach depends on operators enabling it and your brand being verified, market by market. Ask for those numbers.
- Keep SMS as a fully designed fallback, and distrust engagement comparisons that lack a proper control group.
- 8The real cost of an unofficial transportUnofficial protocol implementations are cheaper, faster to launch and genuinely useful. They also transfer a risk to the business using them that should be priced and disclosed.
- Unofficial WhatsApp connections are cheap and quick, but the account can be restricted without notice, and the business that owns it carries that risk.
- Judge the choice by what happens on the day access stops, not by the monthly saving.
- If you use one, disclose it, keep your own copy of conversations, and have the official route ready to switch on.