SIP Trunking for Voice AI
SIP trunking is the protocol that lets a voice AI platform send and receive phone calls over the internet, connecting to the public phone network via a carrier like Twilio or Vobiz.
SIP (Session Initiation Protocol) trunking is how voice AI platforms connect to the public phone network. A SIP trunk is a virtual phone line over the internet, provided by a carrier like Twilio, Vobiz, Exotel or Telnyx. The voice AI platform sends and receives calls through the SIP trunk, and the carrier handles the actual PSTN connectivity. For Indian deployments, SIP trunks must be paired with DLT-registered caller IDs to be compliant.
How SIP trunking works with voice AI
When a phone call arrives at your SIP trunk (inbound) or your voice AI agent wants to dial out (outbound), the audio is streamed over the SIP trunk as RTP packets. The voice AI platform plugs into this stream, runs STT + LLM + TTS in real time, and sends the agent's audio back over the trunk. Modern voice AI platforms like ThinnestAI handle the SIP complexity automatically.
Why it matters
SIP trunking is what separates a voice AI agent you can only reach through a web page from a voice AI agent you can reach by dialing a real +91 phone number. Without SIP, there is no phone call.
More definitions
A voice AI agent is an AI-powered system that has real-time spoken conversations — over a phone call, a web widget or a SIP trunk — using speech recognition, a language model and speech synthesis.
Voice AI is the umbrella term for AI systems that understand and generate human speech in real time — powering voice assistants, phone agents, voice chatbots and real-time translation.
Conversational AI is the category of AI systems designed to interact with humans in natural language, across chat, voice, email and messaging — using NLU, LLMs and tool-calling to hold multi-turn conversations that actually accomplish work.
IVR is a rigid scripted decision tree (press 1 for sales). Voice AI is a natural-language agent that understands free-form speech, uses LLM reasoning, and calls tools to take real actions.
BYOK means you bring your own API keys for the LLM, STT and TTS providers, and the voice AI platform routes usage through your accounts instead of bundling the provider costs into its own pricing.
BYON means you bring your own phone number — via a Twilio, Vobiz or Exotel account — and connect it to the voice AI platform via SIP, instead of renting a number from the platform itself.