Every business already communicates on several channels. The difference between "multichannel" and "omnichannel" is whether those channels know about each other. A customer who confirmed on WhatsApp should not get a voice reminder asking them to confirm. A customer who never opens email should get the offer on RCS instead.

Here is a way to design it.

Step 1: List the moments, not the channels

Start from the customer's timeline. For an online retailer:

1. Sign-up
2. Verification (OTP)
3. First order confirmation
4. Shipping and delivery updates
5. Delivery feedback
6. Re-engagement after 30 days of inactivity
7. Loyalty and renewal

Each moment has a job: inform, verify, confirm, sell, retain.

Step 2: Match each moment to a primary channel

Moment	Primary	Why
OTP	SMS	Fast, universal
Order confirmation	WhatsApp	Buttons, replies, history
Delivery updates	WhatsApp → SMS fallback	Reach everyone
Product discovery	RCS or WhatsApp	Rich cards, carousels
Detailed onboarding	Email	Room for content
Unresponsive reminder	Voice	Confirms attention
Win-back offer	WhatsApp + Email	Rich, personal, measurable

The rule: choose by what the customer needs to do at that moment, not by what is cheapest.

Step 3: Add fallback rules

Define what happens when the primary channel fails or is not available:

• WhatsApp not delivered in 30 seconds → send SMS.
• Email not opened in 48 hours → send a short RCS/SMS nudge.
• Reminder not confirmed one day before → voice call.

Fallbacks are where most of the reliability comes from.

Step 4: Share state across channels

The system that sends messages needs to know the customer's status: confirmed, rescheduled, opted out, replied. That is what prevents duplicate reminders and contradictory messages. In practice it means one customer record and one event log that every channel reads and writes.

Step 5: Respect preferences

Let customers pick channels where it is reasonable ("Get updates on WhatsApp"), honour opt-outs everywhere, and keep frequency sane. A customer who receives the same offer on three channels in one hour unsubscribes from all three.

What to measure

• Delivery rate per channel and per fallback step.
• Response rate per moment (confirmations, replies, clicks).
• Time-to-resolution for support conversations.
• Opt-out rate — the early warning for over-messaging.

A worked example

A clinic sends an appointment confirmation on WhatsApp with Confirm / Reschedule. Two days before the appointment, unconfirmed patients get an SMS. One day before, still-unconfirmed patients get a voice call with press-1-to-confirm. Confirmed patients get a final SMS with the address. The result is fewer no-shows and far fewer calls made by staff.

We build these journeys across SMS, WhatsApp, RCS, Voice and Email. Talk to an expert to map yours.