WhatsApp Business
Meta's business version of WhatsApp — free app for small businesses + WhatsApp Business API (paid, via partner) for enterprise/chatbots.
200M+ daily business users. The dominant customer-service channel in Latin America, India, Africa, the Middle East. API flow: messaging conversation is billed per session (24h window). 2024: WhatsApp Business accounts can take payments (WhatsApp Pay, first in Brazil + India).