Retell AI

Retell AI is a managed voice agent platform that assembles a full STT-LLM-TTS pipeline behind a single API, enabling developers to deploy production phone agents in hours rather than weeks. Its modular billing starts at $0.055 per minute for voice infrastructure and adds LLM, TTS, and telephony components separately, with a minimum all-in rate starting at $0.07 per minute for the standard configuration. The platform supports BYO-LLM and BYO-TTS, integrating with OpenAI, Anthropic, Groq, and local models for the LLM layer, and ElevenLabs, Cartesia, OpenAI, Minimax, and others for TTS. SIP trunking is included at no charge, and Twilio or Telnyx can be used for managed phone numbers across 15-plus countries. Turn-taking, barge-in detection, and conversation state management are handled natively by the Retell layer, abstracting away cascade orchestration complexity. Retell AI is well-suited for high-volume telephony operators running outbound sales, appointment reminders, or customer support at scale. Its $10 free credit onboarding, transparent second-based billing with no charge for failed connections, and 4.8-star G2 rating across more than 2,200 reviews make it the most field-validated voice agent platform for telephony use cases.