Phone-call APIs for AI assistants: carrier, runtime and application layers

A phone-call API can initiate or control a telephone connection, but it does not automatically provide a useful AI assistant. You also need audio handling, conversation logic, safe business actions and an application that records what happened.

Separating these responsibilities makes it easier to choose a managed platform or build an application without recreating work a runtime already provides.

Map the call path

Caller and telephone network
        ↕
Carrier number and call route
        ↕
Voice runtime and media session
        ↕
Conversation model and permitted business actions
        ↕
Application records, permissions and accounting

This is a conceptual diagram, not an API schema. Implementations differ, and some products combine several layers.

Carrier APIs and SIP solve related problems

Carrier call-control APIs expose provider-specific operations and events. SIP trunking supplies a standard signaling path between telephone infrastructure and a voice service. Choosing SIP does not remove carrier configuration, authentication or number eligibility requirements.

Consult Twilio's SIP documentation and Telnyx's SIP overview for their respective setup. Use LiveKit telephony for the runtime side.

Do not confuse the runtime with the finished application

A voice runtime can handle media sessions and voice interactions, while your application still owns tenant authorization, selected configuration, tool permissions, call history and financial controls.

Burki's current architecture uses LiveKit for voice. That avoids treating every new provider as a reason to build another custom audio stream, but it does not remove the need to validate carrier routes and application behavior.

Design business actions for retries

Telephone events and business-system responses may arrive late or more than once. Give an external action a stable request identity, record its result and avoid blindly repeating a side effect after a timeout.

For a booking, distinguish “request sent,” “booking created” and “confirmation delivered.” If the response is ambiguous, reconcile with the business system before issuing another creation request. The assistant should speak only the result the system actually knows.

Acceptance needs more than an API success code

Verify two-way conversation, caller interruption, corrections, a meaningful action, hangup and cleanup. For handoff, test success, rejection and timeout. Check the actual caller experience and inspect every call leg afterward.

A successful request to start a call is not proof that it was answered, that audio flowed or that the business task succeeded. Preserve those separate stages in your records.

Choose how much to own

A managed application can reduce product and operating work; a runtime-based build can provide control when your requirements justify it. Include deployment, monitoring, support and billing in the decision, not only provider API prices.

Start with a narrow use case and a bounded test budget. The platform selection guide and SIP setup checklist help turn this architecture into an actionable evaluation.