Configure a Twilio Elastic SIP Trunk with origination URIs and a termination domain

In-depth guide

Steps

1. In Twilio Console, go to Elastic SIP Trunking and create a new trunk; give it a friendly name and note the automatically generated SID.
2. Under the Termination tab, assign a termination SIP URI subdomain (e.g., yourcompany.pstn.twilio.com) — this is the address your PBX dials to send calls out to the PSTN through Twilio.
3. Add IP Access Control Lists or Credential Lists to authenticate your PBX; Twilio Elastic SIP Trunks do not support SIP REGISTER, so you must add your PBX's source IP(s) as trusted peers in the Access Control List.
4. Under the Origination tab, add your PBX's SIP URI as an origination URI so that Twilio delivers inbound PSTN calls to your PBX; set the priority and weight for failover across multiple URIs.
5. Associate phone numbers or a Twilio-hosted CNAM/E.164 number with the trunk under the Numbers tab, or use the trunk SID in a BYOC number configuration.
6. Twilio Elastic SIP Trunks support G.711 (PCMU/PCMA) natively; if your PBX offers additional codecs such as G.729, ensure your SBC or PBX is configured to prioritize PCMU to avoid transcoding or codec mismatch errors.