Map Twilio terminology onto your PBX
Twilio uses termination for calls your infrastructure sends to the PSTN and origination for calls delivered from its numbers to your infrastructure. Establish both directions in the design. A successful outbound pilot does not establish an inbound destination.
Keep a record of the trunk, associated numbers, public entry point and the administrator who controls each. If an SBC terminates the carrier connection, its accepted settings and the PBX-facing settings are separate evidence.
Documented service facts
Reviewed 2026-09-08. Compare SIP trunk services →
Outbound authentication
DocumentedIP access lists, credential lists, or both; when both are configured, both are enforced.
SIP registration
DocumentedConfigure this service without SIP REGISTER. Credentialed termination is distinct from endpoint registration.
Inbound delivery
DocumentedAssociate numbers with a trunk and configure origination SIP URIs pointing to your PBX or SBC.
Inbound failover
DocumentedMultiple origination URIs with priority and weight; response-dependent fallback.
Number and regional availability
Not verifiedInternational number selection is documented; exact country, number inventory and port eligibility for your account are not verified.
Audio codecs
DocumentedPCMU and PCMA are generally available; G.729, Opus and AMR-NB have limited availability.
T.38 fax
Not verifiedNot verified for this exact service in this review. Do not infer fax support from another Twilio product.
Signaling and media encryption
DocumentedSecure Trunking documents TLS and SRTP for the trunk connection.
Call-start capacity
DocumentedDefault termination rate is 1 new call per second per trunk per region; increases have a separate process and pricing.
Emergency calling
DocumentedDocumented in specified countries; address association, valid calling number and callback routing must be configured.
Pricing model
DocumentedUsage-based calling, separate number rental and optional features; destination, country and committed-use terms affect cost.
Administration and support
Not verifiedConsole and REST API documentation are available. Contracted support response times and your service commitments are not verified.
SMS and MMS
Not verifiedNumber-specific messaging eligibility, registration requirements and charges are not verified in this trunk review.
Do not wait for a registration indicator
Elastic SIP Trunking uses a configured connection model without REGISTER. Read the authentication facts above before selecting a PBX template. A credential list for outbound challenges does not imply that the trunk must appear as a registered endpoint.
Verify an outbound request with the intended identity and inspect an inbound call arriving at the configured destination. Use the exact-version PJSIP controls in a managed PBX. The main Twilio page still contains historical Asterisk 13 examples; those are not an Asterisk 22 installation procedure.
Distinguish capacity from call-start rate
Twilio documents a CPS limit separately from ongoing call capacity. A burst of many new calls can therefore behave differently from the same number of already established calls. Size the permitted start rate using the actual busy-period pattern.
Use bounded authorized load tests, record the responses, and confirm the account’s active limits before a migration. Do not interpret an elastic-capacity headline as permission to generate unlimited new calls in one instant.
Check media and resilience explicitly
The current codec page distinguishes generally available and limited-availability codecs. Confirm which are enabled for the account and what is negotiated on the carrier leg. A wideband phone does not guarantee a wideband PSTN path.
For resilience, test inbound fallback and outbound destination failover separately. Inspect which response triggers another attempt. A reachable PBX returning a deliberate rejection can behave differently from a silent destination.
Resolve launch-specific questions
For emergency calling, confirm country eligibility, number identity, address status and inbound callback handling using the dedicated provider documentation. Use its approved test process. Keep emergency routing independent of ordinary international dialing permissions.
For commercial review, obtain the rate schedule for the actual destination mix and include number and feature charges. Port eligibility, T.38 requirements, messaging workflow and support commitments remain explicit questions for the exact service order.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.
- Twilio trunk configuration ↗
- Twilio codec availability ↗
- Twilio call-start limits ↗
- Twilio emergency configuration ↗
- Twilio US pricing context ↗
Examples require adaptation to your topology. No live PBX or hardware testing is claimed.