How to Connect Your Existing SIP Trunk to a Voice AI Agent

Connecting your existing SIP trunk to a voice AI agent is the most reliable way to run automated business calls on your own telephony infrastructure. Bolti, a voice AI platform for building production-ready conversational phone agents, allows you to link your current carriers like Twilio, Plivo, and Exotel directly to intelligent voice agents. You can start building today with a 50-minute free trial, or scale your production operations with our transparent pricing starting at ₹7/minute pay-as-you-go.

By integrating your existing telecom contracts, you maintain full control over your phone numbers, routing rules, and carrier relationships while gaining access to sub-second latency voice interactions.

How do you connect a SIP trunk to a voice AI agent?

Connecting your SIP trunk to Bolti involves linking your existing telephony provider (like Twilio, Plivo, or Exotel) to the platform and assigning your DID numbers to specific AI agents. This lets you keep your current carrier contracts and phone numbers while routing calls directly to AI agents.

When a customer dials your number, the call travels through your telecom carrier to Bolti's real-time voice pipeline. Bolti processes the call using four coordinated layers:

• STT (Speech-to-Text): Transcribes the caller's spoken words into text. Bolti supports low-latency engines like Deepgram, Cartesia, and Fennec (specifically optimized for Indian languages like Hindi, Tamil, and Telugu).
• LLM (Large Language Model): The brain of the agent. It reads the transcript, decides what to say, and triggers any connected database tools. You can use Groq (Llama-family models) for ultra-low latency, or OpenAI GPT-4o and Google Gemini 2 Pro for complex reasoning.
• TTS (Text-to-Speech): Synthesizes the natural-sounding voice reply. Providers like Cartesia, ElevenLabs, and SarvamAI (best-in-class for Indic voices) power this layer.
• Telephony (SIP/PSTN): Carries the synthesized audio back to the caller over your connected SIP trunk.

Because these components work together in real-time, Bolti achieves sub-second turn-taking and handles real interruptions seamlessly, making the conversation feel natural to the caller.

Why should you bring your own SIP trunk (BYOC)?

Bringing your own carrier (BYOC) lets you maintain your existing telecom relationships, secure volume-based pricing, and comply with local regulations. Instead of buying new numbers, you use your established infrastructure to power your AI voice interactions.

Using BYOC with Bolti offers several distinct operational advantages:

• Negotiated Rates: If your business handles lakhs of calls monthly, you likely have custom volume pricing with Exotel, Plivo, or Twilio. BYOC ensures you keep those exact carrier rates.
• Zero Number Porting Hassle: There is no need to port your highly advertised customer support or sales numbers to a new provider. You simply point your existing numbers to Bolti.
• Local Telecom Compliance: Keeping your existing trunks makes it easier to align with regional guidelines, such as the Indian DPDP Act, GDPR, or HIPAA regulations.
• Outbound Caller ID Control: You retain the ability to manage verified caller IDs, preventing your automated outbound calls from being flagged as spam by telecom carriers.

Which telephony providers does Bolti support?

Bolti natively supports major Indian and global telephony providers, making it easy to wire your existing numbers. You can connect Twilio, Plivo, Exotel, or Vobiz directly from your dashboard under the provider settings.

Depending on your target audience and geographic location, you can choose the provider that fits best:

• Exotel: The preferred choice for businesses operating in India. Exotel provides excellent domestic routing, high call-completion rates, and reliable virtual numbers across Indian cities.
• Plivo: A highly competitive global cloud communicator. Plivo offers great rates for both Indian and international voice termination, with quick SIP trunk setup times.
• Twilio: The global standard for developer-friendly SIP trunking. Twilio is ideal if you operate across multiple countries and require a highly resilient, globally distributed telephony network.
• Vobiz: A robust enterprise voice provider suited for specialized corporate setups and dedicated SIP trunk integrations in India.

If you do not want to use an external provider, you also have the option to buy phone numbers directly from Bolti. These are provisioned on our managed trunks and appear automatically in your workspace.

How do you assign a phone number to an AI agent?

Once your SIP trunk is connected to Bolti, you assign numbers to your agent in the Phone tab of the agent's settings. The change takes effect immediately, routing the next incoming call directly to your voice agent.

To assign a number, follow these steps:

1. Navigate to your agent's detail page in the Bolti dashboard.
2. Click on the Phone tab.
3. Scroll down to the Assign New Number panel.
4. In the Select Trunk dropdown, choose your connected SIP trunk (e.g., your Exotel or Twilio account).
5. In the Select Phone Number field, enter your DID number.
6. Ensure the number is in strict E.164 format (it must start with a + and the country code, such as +919876543210). Bolti will reject numbers missing the plus sign or country code.
7. Click Assign Number.

Once assigned, the number will appear in the top section of the Phone tab with an "Assigned" badge. You can unassign or reassign numbers to different agents at any time from the Phone Numbers page in the left navigation menu.

How can you test your voice agent before routing live calls?

You can test your voice agent's prompts, tools, and voices without spending telephony minutes by using Bolti's built-in Preview tab. This runs the identical AI stack directly through your browser's microphone and speakers.

Testing in the Preview tab ensures your agent works perfectly before you connect it to a live SIP trunk:

• No Telephony Costs: Because the audio travels over your internet connection instead of a phone network, you do not pay telephony carrier fees during testing.
• Identical AI Behavior: The preview uses the exact same STT, LLM, TTS, custom prompts, and database tools that run on production phone calls.
• Isolated Sessions: Each preview connection is fully isolated. When you click disconnect, the conversation history is cleared, letting you start fresh on your next test run.

This workflow allows you to iterate on your system prompts, test how the agent handles user interruptions, and preview different voices (like SarvamAI's Anushka for Hindi or Cartesia's Blake for English) instantly.

Set up your first voice AI agent with your SIP trunk

Ready to scale your business communications? You can sign up for a free Bolti account and get 50 free minutes of call time to test your setup. If you need help configuring custom SIP trunks or integrating enterprise-grade telephony, you can contact our team for dedicated technical support. Wire your Exotel, Plivo, or Twilio numbers in under 10 minutes and start handling calls automatically in 2026.

Frequently Asked Questions

What is E.164 format and why does Bolti require it?

E.164 is an international telephone numbering standard that ensures each phone number has a unique global address. It starts with a plus sign (+) followed by the country code and the subscriber number (for example, +919876543210). Bolti requires this format to prevent routing errors across different global carriers.

Can I use different SIP trunks for inbound and outbound calls?

Yes. Inbound calls are routed based on the specific numbers you assign to your agent in the Phone tab. Outbound calls do not require pre-assignment; you can select any outbound-capable trunk connected to your workspace at the time you trigger the dial API or use the outbound dashboard.

Will bringing my own SIP trunk reduce call quality?

No. Bringing your own SIP trunk (BYOC) maintains the native voice quality of your carrier. Bolti uses telephony-grade noise cancellation and low-latency processing to ensure that the audio transmitted back and forth over your trunk is clear and responsive.

Can I use custom cloned voices over my SIP trunk?

Yes. By using the Custom mode in the Voice tab, you can input manual voice IDs from providers like ElevenLabs. This allows you to use your own custom cloned voices for all calls routed through your SIP trunk.