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VoiceInfra AI agents register on your existing PBX as standard SIP extensions — the same way a desk phone or softphone does. There is no hardware to swap out, no carrier to change, and no downtime. Your phone system keeps running exactly as it does today, and your AI agent simply occupies an extension that you assign.

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Compatible PBX Systems

VoiceInfra works with any PBX that supports standard SIP registration. The table below lists commonly deployed systems, but if your PBX speaks SIP it will work.
PBX SystemNotes
3CXAll editions (SMB, Pro, Enterprise)
YeastarP-Series, S-Series, and Cloud PBX
FreePBX / AsteriskAny version with SIP/PJSIP support
VicidialRequires SIP extension permissions
IssabelFully supported
AvayaAura and IP Office with SIP trunking
CiscoCUCM and Cisco UCM via SIP
MitelMiVoice and MiCloud
Any SIP-capable PBXIf it supports RFC 3261, it works
Whitelist IP 51.81.221.91 before registering. Without this step, SIP registration will fail. Add this IP to your PBX firewall or allowed IP list first — then proceed with the steps below.

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Set Up a PBX Extension

1

Create a new extension on your PBX

In your PBX admin console, create a standard SIP extension exactly as you would for a new desk phone or softphone. Note the extension number, SIP username, and SIP password — you will need them in VoiceInfra.
2

Whitelist the VoiceInfra IP

Add IP address 51.81.221.91 to your PBX firewall’s allowed IP list (sometimes called an IP ACL or trusted host list). This allows SIP traffic to flow between your PBX and VoiceInfra servers. This step is required. Without it, the extension will not register.
3

Register the extension in VoiceInfra

Open the VoiceInfra dashboard and navigate to Settings → Phone Numbers → PBX Extensions → Add Extension. Fill in the following fields:
  • Display Name — a human-readable label (e.g., “Reception AI”)
  • Extension Number — the extension number from your PBX
  • PBX Domain — your PBX’s SIP domain or IP address
  • SIP Username — the SIP username from your PBX extension
  • SIP Password — the SIP authentication password
  • Call Direction — choose Inbound, Outbound, or Both
4

Configure advanced SIP settings (optional)

Expand the Advanced Settings section if your PBX environment requires custom routing. You can set:
  • SIP Proxy — for environments that route SIP through an intermediate proxy
  • Registration Proxy — if your PBX requires a separate registration endpoint
  • Transport Protocol — choose TCP, UDP, or TLS to match your PBX configuration
5

Assign to an agent

After the extension registers successfully, select which AI agent handles calls on this extension. The agent is now live — inbound calls ring the AI, and the AI can place outbound calls from the extension.

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Call Directions

Choose how each extension handles calls when you set it up.
DirectionBehavior
InboundThe AI agent answers calls that arrive on this extension
OutboundThe AI agent places calls using this extension as the originating number
BothThe AI agent handles both incoming and outgoing calls
You can change the call direction at any time from the extension settings page. Changes apply immediately without re-registering.

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Configuration Reference

FieldDescription
Display NameHuman-readable label for this extension in VoiceInfra
PBX DomainYour PBX’s SIP domain or IP address (e.g., pbx.example.com or 192.168.1.10)
SIP UsernameThe extension number or username from your PBX (digits only)
SIP PasswordSIP authentication password from your PBX extension
TransportTCP, UDP, or TLS — match this to your PBX’s SIP transport setting

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Frequently Asked Questions

No. Adding a SIP extension to a PBX is a non-destructive operation. Your existing extensions, call routing, and ring groups are completely unaffected. There is zero downtime.
Unlimited. You can register as many extensions as your PBX supports — one per AI agent, multiple agents per PBX, or agents across multiple PBX systems.
Yes. Set the call direction to Both when configuring the extension. The same AI agent will answer incoming calls and place outgoing calls using that extension number.
Yes. VoiceInfra encrypts all SIP credentials at rest. Credentials are never exposed in logs, API responses, or the dashboard UI after you save them.
Check three things: (1) confirm IP 51.81.221.91 is whitelisted in your PBX firewall, (2) verify your PBX domain, SIP username, and password are correct, and (3) ensure the transport protocol (TCP/UDP/TLS) matches your PBX configuration.
Yes. Update display names, SIP credentials, call direction, or advanced proxy settings at any time from Settings → Phone Numbers → PBX Extensions. Changes take effect immediately.