How to Connect an AI Voice Agent to a SIP Trunk

How to Connect SIP Trunk?

To connect an AI voice agent to a SIP trunk, you add your carrier's trunk details to the voice platform, point a campaign at that carrier, and place a test call. A SIP trunk is the internet connection to a phone carrier that lets your AI voice agent place calls to regular phone numbers. This guide walks through the steps for outbound calling with VoiceOI, then lists what to ask your carrier and what to test.

What a SIP trunk does for an outbound AI voice agent

When a bot calls someone, the call has to reach the phone network. The SIP trunk is that path. The AI platform speaks SIP to your carrier, and the carrier connects the call to the number you are dialing. The carrier bills the minutes. VoiceOI bills the bot, per bot per month, so the two costs stay separate.

Over the same trunk, a bot campaign runs the dialing, answering-machine detection and live transfers to your closers. Pricing is per bot, which is per concurrent call, so the number of bots you run and the number of channels your carrier allows both limit how many calls can happen at once.

What you need before you start

An account with a SIP carrier. VoiceOI works with any SIP carrier, including Twilio and Telnyx trunks, or an Asterisk or FreePBX system that speaks SIP.
Outbound calling enabled and funded on that account.
Caller ID numbers that belong to you and are allowed by your carrier.
Consent for the people you will call. See the compliance note below.
A script to test with, even a short one.

VICIdial or Asterisk vs hosted SIP: which connection do you use?

VoiceOI prices bots by connection type, and the connection decides what you configure:

Connection	What you configure	List price per bot per month
VICIdial / Asterisk	Bots connect to your VICIdial or Asterisk/FreePBX system. Confirm with the VoiceOI team how your carrier is set up in this case.	Fronter from $25, LG from $50, Closer from $100
Hosted SIP	You add a SIP carrier in the Carrier Manager, as in the steps below. The tier lists a Dedicated Switch.	Fronter from $45, LG from $70, Closer from $120

The steps below add a carrier to the Carrier Manager and attach it to a campaign. Check with the VoiceOI team which connection fits your setup, and see pricing for each tier.

Steps to connect an AI voice agent to a SIP trunk

Choose where the trunk comes from. You can use an existing carrier trunk, a new Twilio Elastic SIP trunk, a Telnyx connection or the trunk on your Asterisk or FreePBX server. See Twilio setup, Telnyx setup and Asterisk setup.
Check the carrier's limits first. Ask for the maximum concurrent channels and calls per second on your account (questions below). Your bot count should not exceed the channels you can use.
Create the trunk for outbound calls at the carrier. Follow your carrier's own guide; see Twilio setup and Telnyx setup. Note the connection details the carrier gives you.
Add your caller ID numbers to the carrier account, following the carrier's rules for numbers you can use on outbound calls.
Add the carrier to VoiceOI. Open the Carrier Manager and paste the carrier's connection block in the sip.conf or pjsip.conf format.
Attach the carrier to a campaign and load a small test list of numbers you control.
Place a test call from a bot to your own phone and listen for audio in both directions, the opening line and the end of the call.
Test the exits. Say a do-not-call phrase and confirm the call ends. Let a call go to voicemail and confirm it ends and is logged as a machine. Qualify yourself and check that the live transfer reaches your closer line with notes.
Scale slowly. Add bots in small batches and watch the realtime view and the recordings.

If you run VICIdial, the carrier step is the same, followed by provisioning remote agents. See the VICIdial AI integration.

Questions to ask your carrier

These are questions for the carrier, not features of any AI platform. The answers decide how the trunk behaves.

How many concurrent channels does my account allow, and can it be raised?
What is the calls-per-second limit? Dialing a large list too fast can be throttled.
How is caller ID reputation handled? Numbers that show as spam reduce answer rates.
What attestation do my calls get under STIR/SHAKEN, and do you need registration for my use?
Are there restrictions on automated or AI-voice calling on my account type?
What does outbound cost per minute to the countries and number types you will call?
Is there a minimum monthly commitment or a per-channel fee?

Common problems

Symptom	Likely cause	What to check
Call never rings	Authentication or wrong address	The block you pasted and the carrier's allowed IPs or credentials
One-way or no audio	Network or firewall	The carrier's audio port range and your firewall
Calls rejected at the carrier	Caller ID not allowed	The number is verified or owned on the account
Fewer simultaneous calls than expected	Channel limit	The carrier's concurrency cap
Many calls fail on a big list	Calls-per-second limit	Slow the campaign down
Calls answered as spam	Caller ID reputation	Ask the carrier about number reputation and attestation

What this setup does not cover

VoiceOI places outbound calls. It is not an inbound receptionist. CRM sync is coming soon, and VoiceOI does not offer a public API. Conversations are English-first. This guide is about the phone connection, not a promise of call quality, which depends on your carrier and network.

Compliance note

A SIP connection does not change the legal rules: the FCC's February 2024 ruling treats AI voices as artificial voices under the TCPA, which generally means prior express written consent for telemarketing. The customer remains responsible for compliance, and this is not legal advice. See TCPA controls for the controls VoiceOI provides.

Frequently asked questions

Can I use my existing SIP trunk? Yes, if your carrier gives you SIP connection details. Add the block in the Carrier Manager.

How many concurrent calls can my trunk carry? That depends on your carrier account. Bots are priced per concurrent call, so run no more bots than your channel limit.

Does it take inbound calls? No. VoiceOI is built for outbound campaigns.

Do I pay per minute to VoiceOI? No AI per-minute fee. You pay per bot per month, and the carrier bills the minutes. See pricing.

For the product page, see SIP trunk for AI voice agents.