Both reach a phone directly without needing an app to be opened first (technically), but they behave very differently once a message actually arrives.
Open Rates and Engagement
WhatsApp messages are typically read within minutes and support replies, media, and buttons within the conversation. SMS is read reliably too, but is a dead-end text with no rich interaction - no images, no quick-reply buttons, no ongoing conversation thread.
Cost Per Message
SMS costs are typically fixed per message regardless of content. WhatsApp Business API pricing is conversation-based, which can be more cost-effective for back-and-forth interactions rather than one-way blasts.
Rich Media and Interactivity
WhatsApp supports images, PDFs, location sharing, and interactive buttons - useful for order confirmations with an attached invoice, or product catalogs. SMS is plain text only.
Which to Use
For any business with a genuine two-way customer relationship (support, order updates, sales conversations), WhatsApp generally wins. SMS still has a place for very short, universal alerts to numbers that may not have WhatsApp. See our WhatsApp Marketing service or get in touch to discuss your specific use case.