What are AI phone agents?

AI phone agents handle inbound and outbound phone calls using voice AI. They listen to callers, understand intent, respond naturally, and can take actions — book appointments, answer questions, transfer to humans, and update records. Technology stack: telephony (Twilio, Vonage), speech-to-text (Deepgram, AssemblyAI, Whisper), LLM reasoning (GPT-4o, Claude), text-to-speech (ElevenLabs, PlayHT, Cartesia), and orchestration platform (Vapi, Retell AI, Bland AI). Capabilities in 2026: natural turn-taking (interrupts and resumes gracefully), emotion detection, multi-language support (switch languages mid-call), real-time tool use (check availability, look up accounts, process payments), and call summarization with CRM sync. Use cases with proven ROI: appointment scheduling (dental, medical, salons — 40-60% labor cost reduction), lead qualification (insurance, real estate — handle 100% of after-hours calls), customer service (order status, returns, FAQs — 70% resolution without human), and outbound campaigns (appointment reminders, surveys, reactivation). Cost: $0.05-0.15 per minute all-in (STT + LLM + TTS + telephony). A 3-minute call costs $0.15-0.45. Human agent equivalent: $1.50-3.00 per call. Limitations: struggles with heavy accents, background noise, and complex emotional situations. Always provide a clear path to human escalation.