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Trunks & Phone Numbers

Trunks & Phone Numbers

SIP trunks are how SIPHON connects to the PSTN (real phone numbers). SIPHON uses trunks for both inbound and outbound calling.

Provider-specific SIP examples (Twilio, Telnyx, Plivo, Wavix): Provider-specific quickstarts

What is a trunk?

A trunk is a set of SIP provider credentials + configuration that SIPHON uses to:

  • receive inbound calls (inbound trunk)
  • place outbound calls (outbound trunk)

In SIPHON docs, you will see:

  • inbound_trunk_id
  • outbound_trunk_id

These are identifiers for the trunks configured in your SIPHON calling setup.

Inbound vs outbound

Inbound trunks

Inbound trunks connect your provider’s inbound number(s) into SIPHON. Dispatch rules typically reference an inbound trunk.

Learn more:

Outbound trunks

Outbound trunks are needed to dial numbers from SIPHON to the PSTN.

SIPHON supports:

  • referencing an existing sip_trunk_id
  • or passing credentials (sip_trunk_setup) so SIPHON can reuse/create the trunk

Learn more:

Phone number fields you will encounter

SIPHON uses a few consistent phone-number concepts.

  • agent_number
    • The number your agent is effectively “calling from” (caller-id).
    • For outbound calls this is typically your SIP number.
  • user_number
    • The customer/caller number.
    • For outbound calls this is number_to_call.
  • number_to_call
    • Outbound-only: the destination number your code is dialing.
  • phone_number
    • Inbound-only: the number that a dispatch rule matches.

Formatting tips

  • Use E.164 format where possible (example: +15551234567).
  • Keep your trunk configuration and provider setup consistent with caller-id requirements.

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