Pre-connect SIP during ring — billing before human answers?

Support Help
1

We use custom telephony (register-phone-call + Telnyx). Today we dial SIP to sip:{call_id}@sip.retellai.com only after the lead answers (call.answered). No answer = no Retell bridge, no charge.

To cut post-answer latency, we’re considering opening the Retell SIP leg during ring and bridging on answer. If no answer, we hang up the orphan SIP leg (~25s max).

Questions:

  1. If SIP connects during ring but the lead never answers — are we billed? Does it show in call activity?
  2. Does the agent (LLM/TTS) start as soon as SIP connects, or only after bridged with the human?
  3. Does this count as 1 or 2 concurrent calls during ring?
  4. Is there a supported way to pre-warm without billing until the human is connected?

Thanks!

2

Hello @scorcezzi Thanks for the detailed context — this helps a lot. Let me go point by point for your dial-to-SIP setup:

  1. Yes, once we 200 OK your INVITE, the call is “connected” on our side. You’ll be billed for the full SIP leg duration and it will appear in Call Activity (typically with disconnection_reason = user_hangup if you send BYE).

  2. The agent stack (LLM/STT/TTS) spins up immediately on 200 OK

  3. It consumes exactly one concurrency slot from INVITE until BYE.

  4. We don’t currently support a pre-warm / early-media mode that avoids billing while the SIP leg is up. The only non-billed window is between register-phone-call and sending the INVITE, but the agent isn’t warmed during that time.

Given your goal (reduce post-answer latency without inflating cost), the best-supported pattern is what you’re already doing: initiate the SIP leg only after the lead answers

Thank You