WhatsApp has 2B+ users globally and dominates in LATAM, India, Southern Europe, and parts of Africa. Open rates exceed 95%. Far above any email channel.
Templated messages (HSMs) require Meta approval but can be sent to opted-in customers at any time. Conversational replies are free within 24 hours of the user's last message.
Callsy uses WhatsApp Business API for booking confirmations, payment reminders, and cart-recovery follow-ups. Especially in regions where WhatsApp dominates voice in customer preference.