To deliver seamless inbound and outbound calling capabilities, CallHQ relies on SIP trunking and virtual phone numbers. These telephony building blocks are critical to enabling real-time communication between your AI agents and end users.

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What is SIP Trunking?

SIP (Session Initiation Protocol) Trunking is a method of delivering voice communication and multimedia sessions over the internet. It replaces traditional phone lines and allows you to make and receive calls via your internet connection.

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Why it matters for CallHQ

  • Reliable: SIP provides a consistent and scalable method to route voice traffic.
  • Real-time: Required for connecting your Voice AI agent with telecom infrastructure.
  • Flexible: Allows you to manage multiple concurrent calls without physical lines.
  • Global reach: Enables calling across geographies using virtual numbers.
CallHQ integrates with SIP providers to establish the bridge between your AI agent (hosted on our platform) and real phone networks worldwide.

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What is a Virtual Number?

A virtual number is a telephone number that isn’t tied to a physical phone line. It exists in the cloud and can be routed to any endpoint, such as:
  • An AI agent (e.g., your CallHQ assistant)
  • A SIP address
  • A VoIP endpoint
  • A call forwarding destination

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Why you need one

  • For inbound calls: Users dial the virtual number, which connects directly to your AI agent.
  • For outbound calls: Your assistant uses this number as the caller ID.
  • For branding: You can use a consistent business number across your assistant experiences.
  • For compliance: Many regions require verified virtual numbers to initiate outbound calls.

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Why It’s Necessary for CallHQ

CallHQ is built to enable real-time, programmable voice AI experiences. To support this:
  • We use SIP trunks to connect AI agents to global telecom networks.
  • We assign or integrate virtual numbers to handle both incoming and outgoing traffic.
  • We help customers provision, verify, and manage these numbers through integrations like Twilio and Plivo, or via CallHQ-managed inventory.

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How to Get Started

To use SIP and virtual numbers with CallHQ:
  1. Use one of our supported telephony integrations: Twilio and Plivo, or via CallHQ-managed inventory
  2. Or, request a number and we’ll provision one for your use case.
  3. Configure the number to point to your assistant’s routing path (via inbound webhook or routing rules).
Need help provisioning a number or setting up SIP for your org?
Talk to our team.