Vapi SIP trunk and phone numbers

Yes. Vapi publishes a dedicated didlogic page in its SIP integration documentation, next to Twilio, Telnyx, DIDWW, Zadarma, Plivo and Amazon Chime SDK. didlogic is also listed in the Vapi partner directory as a Technology Partner under Telephony / CPaaS.

Whichever region your Vapi organization is hosted in, and then keep everything on that side. US organizations use sip.vapi.ai; EU organizations use sip.eu.vapi.ai and create their credential and BYO number through api.eu.vapi.ai rather than api.vapi.ai. Mixing an EU API region with the US SIP host is a common cause of calls that never arrive.

Your number and your Vapi SIP trunk credential ID: YOUR_NUMBER@YOUR_CREDENTIAL_ID.sip.vapi.ai, or ...sip.eu.vapi.ai in the EU. Use the credential ID, not your Vapi private API key. Set it in the didlogic portal under the number’s destination, with destination type SIP URI, and keep it at the top of the destination list if you have others configured.

The regional gateway closest to where your traffic originates, for example sip.nl.didlogic.net. The full list is in our outbound calling guide. Use port 5060 unless you specifically need TLS, in which case use 5061.

The most common cause we see is the trunk configured on port 5061 without TLS, where it should be 5060. Check the port and the outbound protocol on the Vapi SIP trunk credential first, before you look anywhere else.

It means two Vapi Phone Number entries are configured with the same phone number, so Vapi receives the inbound call and cannot decide which one owns it. Delete the duplicate Phone Number and the trunk it sits on, and the call routes normally.

Vapi signals from a small set of static IP addresses. If a run of authentication attempts fails, our platform blocks that source IP for five minutes, which affects the shared address rather than just your account. Fix the credentials, or ask us to move you to IP-based authentication with a technical prefix, which removes password authentication from the path entirely.

Not in place. Vapi does not currently allow a Phone Number to be moved between SIP trunk credentials, so you delete the number in Vapi and create it again against the new trunk.

Yes, with conditions. SIP REFER is disabled by default on didlogic accounts and has to be enabled for you, so ask before you build against it. Once it is on, create a Transfer Call tool in Vapi with a SIP destination in the form sip:+E164_NUMBER@YOUR_DIDLOGIC_GATEWAY and keep Blind Transfer selected, which is what makes Vapi send a REFER. Inbound calls can only be referred to another number purchased on your own didlogic account; anything else returns 403 Forbidden. Outbound transfers support PSTN numbers only. If a REFER fails, the call drops rather than returning to the original party.

As two legs. The original leg is billed at its own rate for the full duration of the call, including the time after the transfer, and appears as two transactions. The transferred leg is billed from the moment of the REFER at the rate of the destination number. Both legs show up as separate entries in your call history, marked with a transfer icon. Inbound calls referred to another number on the same account are not billed twice for the internal move unless that destination forwards on to the PSTN.

On the Vapi side, its signalling IPs on ports 5060 and 5061, and UDP 40000 to 60000 for RTP media. Vapi publishes the current addresses per region in its networking and firewall reference, and they differ between US and EU, so read them from there rather than copying them from a blog post. On the didlogic side, allow RTP audio on ports 10000 to 20000 from any IP, because our media IPs are numerous and change, and allow signalling by DNS name rather than static IP. If you cannot allow inbound RTP from any IP, contact support and we will share a specific list.

Yes. Contact support and we will create a dedicated SIP account with IP authentication for you. Worth knowing that Vapi does not generally recommend IP-based authentication on shared SBCs unless the provider issues a unique termination URI, so username and password remains the simpler default for most setups.

G.711 u-law (PCMU), G.711 a-law (PCMA), G.729 and GSM. You can force a specific codec on your side and our SBC will comply where possible. G.722 wideband is supported but its availability is limited and many carriers do not preserve it end to end. For DTMF we support in-band and RFC 2833 / RFC 4733 RTP events.

Yes. Vapi-managed free numbers are US area codes only and capped at five per account, and international numbers are not included. didlogic sources local and toll-free numbers in 140+ countries, with licensed local voice in 17. Once the number is on your didlogic account it imports into Vapi like any other BYO SIP trunk number.

Yes. Paperless porting in eight countries and porting in 60+ more, with ports scheduled to avoid downtime. Porting is available on Business and Wholesale level accounts. A common pattern is porting numbers off another carrier to didlogic while keeping that carrier for SMS or other rails. Vapi’s BYO setup does not care which carrier owns the number.

On calls that stay on a regional path, 80% add under 20 ms of network latency. Your end-to-end conversational latency is dominated by Vapi routing and your STT, LLM and TTS providers, which sit above the transport layer. Choosing the didlogic gateway and the Vapi region closest to your traffic is the part you control at the carrier layer.

Coverage and billing model are the two differences that matter. Local and toll-free numbers in 140+ countries with licensed local voice in 17, against a smaller direct footprint, and no per-channel charges on the carrier side. The Vapi platform fee is the same either way. See the Twilio alternative for AI voice page.

You pay for numbers, inbound minutes and outbound termination. New accounts start with 30 days at no monthly minimum. See call rates and account levels.

Vapi’s DIDLogic guide and our own guide. Engineering support is at [email protected].