How much does it cost?

You pay us only for call minutes on the volai line: inbound 0.50 CZK/min (~EUR 0.02), outbound 0.92 CZK/min (~EUR 0.04), plus the monthly number fee. The agent surcharge (2.50 CZK/min (~EUR 0.10)) does not apply to your own platform. You pay Vapi separately under its own pricing.

Why does the call end right away with no record in Vapi?

Vapi rejects the call before it creates a record. Most often the address uses a bare sip.vapi.ai instead of .sip.vapi.ai, a Vapi organization in the EU region is missing .sip.eu.vapi.ai, or the trunk's gateways do not allow our IP: it needs IP 81.31.45.0 with netmask 24, not the default 32.

Can Vapi also make outbound calls from the Czech number?

The principle is the same as with ElevenLabs (a relay connection before each call), but with Vapi we have so far verified only the inbound direction. Make a test call before you build a campaign on it, and contact support if you get stuck.

SIP trunk

A Czech number for your Vapi assistant

Vapi's free numbers are US only. With a BYO SIP trunk you can put a real Czech number from volai in front of it: callers dial a Prague or Brno number and your Vapi assistant answers.

Don't have a number yet? Compare the ways to get a Czech or Slovak number.

1Get a number at volai

Sign up at volai.cz, top up your credit and pick a Czech number in the portal (Numbers) or through the API. In the portal every number has a “Bring your own agent” guide with a Vapi tab that shows all the values below already filled in.

2Create a BYO SIP trunk in Vapi

In Vapi, create a BYO (bring your own) SIP trunk and add our signalling range 81.31.45.0/24 to its allowed addresses (gateways). Vapi takes the address and the mask separately: IP 81.31.45.0, netmask 24, with inbound calls enabled. With the default mask of 32, Vapi would allow a single address only and reject our calls. Vapi assigns the trunk an ID (credentialId), which you need in the next step. Then import your volai number to the trunk in Vapi in the +420... format and assign an assistant to it.

3Route the volai number to Vapi

Switch the number to SIP mode and set the destination to sip:<your number>@<credentialId>.sip.vapi.ai. If your Vapi organization is in the EU region, the address is <credentialId>.sip.eu.vapi.ai. A bare sip.vapi.ai only works for Vapi's native numbers, not for a number from us. Leave the username and password (sipUsername, sipPassword, in the portal the PBX username and password fields) empty: Vapi recognises our calls by the IP in the gateways, and with a login the call never connects, so volai rejects that setup.

bash

curl -X PATCH "https://volai.cz/v1/numbers/+420601234567" \
  -H "Authorization: Bearer vk_YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{"routing": {
        "mode": "sip",
        "sipUri": "sip:+420601234567@YOUR_CREDENTIAL_ID.sip.vapi.ai"
      }}'

4Call the number and check the status

Call the Czech number from a mobile phone. Your Vapi assistant should answer and the call shows up as inbound in the volai call history. If the call ends right away and Vapi has no record of it, check the credentialId and the region in the address, the IP and mask in the trunk's gateways, and the number import in Vapi.

5Outbound calls via relay (not yet verified with Vapi)

For the outbound direction, fetch the outbound trunk details from GET /v1/numbers/{e164}/sip and create a relay connection with POST /v1/relay right before the call. Platforms that dial a full SIP URI use the sipUri from the response (in Vapi, the customer.sipUri field). We have verified this direction live only with ElevenLabs. If it doesn't work with Vapi, contact support.

bash

curl -X POST https://volai.cz/v1/relay \
  -H "Authorization: Bearer vk_YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{"to": "+420777123456", "from": "+420601234567"}'

What you can do with it

Your Vapi assistant on a Czech number

Your prompt, tools and voice stay in Vapi. Callers dial a regular Czech number instead of a US one, and you get call history, credit and a CZK invoice in one place.

A number you keep

The number is yours whatever platform runs behind it today. Switch it to ElevenLabs, your own PBX or volai's built-in agent by changing one SIP address.

Vapi for inbound, volai for campaigns

On the same account you can keep inbound calls on Vapi and run outbound campaigns from a contact list through volai's outbound tasks.

Frequently asked questions

How much does it cost?: You pay us only for call minutes on the volai line: inbound 0.50 CZK/min (~EUR 0.02), outbound 0.92 CZK/min (~EUR 0.04), plus the monthly number fee. The agent surcharge (2.50 CZK/min (~EUR 0.10)) does not apply to your own platform. You pay Vapi separately under its own pricing.
Why does the call end right away with no record in Vapi?: Vapi rejects the call before it creates a record. Most often the address uses a bare sip.vapi.ai instead of <credentialId>.sip.vapi.ai, a Vapi organization in the EU region is missing .sip.eu.vapi.ai, or the trunk's gateways do not allow our IP: it needs IP 81.31.45.0 with netmask 24, not the default 32.
Should I fill in a username and password?: No, leave both fields empty for a BYO trunk. Vapi recognises our calls by the IP in the gateways, and with a login the call never connects, so volai does not save a username and password for a <credentialId>.sip.vapi.ai address.
Can Vapi also make outbound calls from the Czech number?: The principle is the same as with ElevenLabs (a relay connection before each call), but with Vapi we have so far verified only the inbound direction. Make a test call before you build a campaign on it, and contact support if you get stuck.

Try it now

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