1. A method comprising: a call router of a multi-tenant communication platform system servicing an outbound voice call request provided by an external server system by establishing a voice call session to a first destination telephony endpoint via a telephone network channel of the platform system; the platform system generating a call router application programming interface (API) resource that includes state of the voice call session; and responsive to an API request that specifies a URI of the generated call router API resource, the platform system providing the external server system with the state of the voice call session in an HTTP message.