Build a Voice AI Agent That Handles Inbound Calls End to End
Answer real phone calls with an AI agent that transcribes, reasons, and responds in natural speech, and knows when to hand off to a human.
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This is a handoff plan, not an automatic integration. Review outputs before the next step. Unlabeled arrows show order, not a verified data format. Use the capability links to explore tool substitutions.
Step 1
Pick Vapi or Retell AI Based on Your Telephony Stack
Both platforms handle the full voice pipeline (speech-to-text, LLM reasoning, text-to-speech) end to end. The real decision factor is which one integrates more cleanly with your existing phone number provider and CRM, not a feature difference between them.
Step 2
Wire Up Real-Time Transcription with Deepgram
Connect Deepgram's speech-to-text API for the inbound audio stream so the agent has an accurate, low-latency transcript of what the caller is actually saying to reason over.
Step 3
Write the Agent's Call-Handling and Escalation Rules
Define what the agent should try to resolve on its own (order status, appointment scheduling, FAQ-style questions) versus a fixed list of triggers that hand off to a human immediately (anger detected, an explicit request for a person, anything touching payment or legal). An agent that doesn't know its own limits is the real customer-experience risk here.
Tools
No catalog tool specified
Step 4
Generate the Agent's Voice with ElevenLabs
Connect ElevenLabs for the text-to-speech side so responses sound natural rather than robotic, which matters more on a phone call than in a chat window since tone is the entire signal.
Step 5
Test on Real Call Scenarios Before Going Live
Run the agent through transcripts of your actual common requests, plus a few deliberately confusing or hostile ones, and confirm it escalates correctly rather than confidently mishandling a call it should have handed off.
Tools
No catalog tool specified
Time Required
1-2 days, one-time setup
Expected Result
A working voice agent that answers real inbound calls, understands callers through real-time transcription, responds with natural speech, and escalates to a human at defined limits instead of improvising past them.
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