What changed
OpenAI made outbound SIP calling available to all organizations through the Live API. A GPT-Live session can dial an E.164 number through a customer's SIP provider while a sideband WebSocket carries call progress, tool events and controls such as DTMF, transfer and hangup.
Why it matters
Voice agents can now initiate phone calls instead of only receiving them, moving telephony, consent, duplicate-event handling and tool execution into the agent's external-action boundary.
What to do
Call one synthetic number through a test trunk, attach the sideband immediately, deduplicate replayed event IDs, test no-answer, transfer and hangup paths, and prove that one call event cannot execute a tool twice before enabling customer calls.
Caveat
Availability does not establish carrier reliability, consent compliance or safe call outcomes. The integration requires a SIP provider, TLS signaling, SRTP media, reachable network ranges and application handling for three-minute ringing and two-hour connected-call limits.