The OpenPhone API is a phone system and communication interface designed for businesses, allowing users to integrate calls, SMS, and contacts more deeply into their tech stack. This API supports automated message sending, keeps contacts synchronized, captures activities in CRM systems, and facilitates custom integrations. It uses API keys for authentication, ensuring secure access to account data and functions. The primary benefits of the OpenPhone API include streamlining system operations, replacing multiple platforms with a single tool, and providing key information previously inaccessible via Webhooks.