SIP Trunking Costs for Voice AI: How to Calculate BYOC Rates

Bolti is a voice AI platform for building production-ready conversational phone agents that helps businesses deploy multilingual voice bots starting with a free trial of 50 minutes. When building a voice AI agent, many teams focus solely on the cost of the artificial intelligence—the Large Language Model (LLM) and Text-to-Speech (TTS) components. However, carrying those calls to real phone lines requires telephony. Understanding how telephony charges and SIP trunking costs for voice AI fit into your overall budget is critical to keeping your cost per minute predictable.

By choosing a Bring Your Own Carrier (BYOC) model, you can connect your own SIP trunks (from providers like Twilio, Plivo, or Exotel) directly to your voice AI runtime. This guide breaks down how to calculate these combined costs so you do not face unexpected billing surprises.

What are the key components of voice AI call costs?

To calculate your total cost per minute, you must look at the four distinct pipeline layers that power every single second of a voice AI call.

Every real-time conversation running on Bolti utilizes a voice pipeline consisting of four major components. Each component carries its own pricing model:

• Telephony (SIP Trunking): Charged per minute by your carrier for routing the call over the public switched telephone network (PSTN).
• Speech-to-Text (STT): Charged per minute (or fraction of a minute) to transcribe the incoming caller audio in real time.
• Large Language Model (LLM): Charged per token (both input prompt tokens and output completion tokens) to process the transcript and generate a response.
• Text-to-Speech (TTS): Charged per character (or per million characters) to synthesize the agent's text response back into high-quality audio.

If you use a bundled provider, these costs are often marked up and packaged into a single flat rate. With a developer-first platform like Bolti, you pay a transparent flat rate of ₹6/minute pay-as-you-go, or you can leverage BYOC to optimize your telephony rates directly with your preferred telecom carrier.

How do you calculate SIP trunking costs for voice AI?

SIP trunking costs are billed directly by your telephony carrier and typically range from ₹0.30 to ₹1.50 per minute for domestic Indian calls, depending on your volume and whether the call is inbound or outbound.

To calculate your pure telephony cost, you need to factor in three main variables:

1. Inbound vs. Outbound Rates

Carriers charge different rates depending on who initiates the call. Outbound calls to mobile phones in India generally cost more than inbound calls to your virtual numbers. Toll-free numbers (e.g., 1800 numbers) incur higher inbound per-minute rates because you, the receiver, bear the entire cost of the connection.

2. Channel Capacity and Monthly Rentals

Most SIP trunk providers charge a monthly rental fee per Direct Inward Dialing (DID) number, alongside a fee for concurrent call paths (channels). If your voice AI agent needs to handle 100 simultaneous calls, you must ensure your SIP trunk is provisioned with at least 100 channels.

3. Connection and Setup Fees

Some traditional telecom operators charge one-time installation or activation fees. Cloud-based SIP providers like Twilio or Exotel usually waive these, charging only small monthly DID rentals.

How does BYOC compare to bundled telephony pricing?

Bringing your own carrier (BYOC) allows you to bypass the standard retail markups that voice platforms place on telephony minutes, which is highly beneficial for high-volume call centers.

Here is a quick comparison of how the two models stack up:

Feature / Cost Factor	Bundled Telephony	Bring Your Own Carrier (BYOC)
Pricing Control	Fixed flat rate set by the AI platform	Negotiated directly with your carrier
Volume Discounts	Limited to platform tier structures	High (scale directly reduces per-minute cost)
Number Portability	Must use platform-provided numbers	Keep your existing business phone numbers
Integration Effort	Zero configuration required	Requires setting up SIP credentials/IP ACLs
Average Telephony Cost	Included in premium markup rates	Pure carrier wholesale rates (approx. ₹0.30 - ₹0.90/min)

For businesses handling tens of thousands of minutes daily, migrating to a BYOC architecture using Bolti’s open API and REST endpoints can cut your telephony bill by 40% or more compared to bundled SaaS alternatives.

How do STT, LLM, and TTS costs add up per minute?

Aside from SIP trunking costs for voice AI, the underlying AI pipeline adds a variable cost based on how talkative your callers are and which AI models you choose.

To estimate your total cost, let us look at the average consumption of an active 1-minute call:

• Speech-to-Text (STT): Providers like Deepgram or Fennec (optimized for Indian accents) cost roughly ₹0.08 to ₹0.15 per minute of processed audio.
• Large Language Model (LLM): An average back-and-forth conversation uses about 1,500 input tokens and 300 output tokens per minute. Using models like DeepSeek-V3.1 on Baseten or GPT-4o-mini, this translates to roughly ₹0.05 to ₹0.20 per minute.
• Text-to-Speech (TTS): Synthetic speech engines like Cartesia or ElevenLabs charge per character. A standard 1-minute agent response contains about 600 characters, costing between ₹0.12 and ₹0.80 depending on the provider quality.

When you add these up alongside your SIP trunking costs, a self-hosted or BYOC voice AI pipeline typically costs between ₹1.20 and ₹2.50 per minute of talk time. Bolti simplifies this math by offering a flat, predictable pricing structure of ₹6/minute pay-as-you-go for the entire stack, removing the headache of managing four separate vendor bills if you prefer a fully managed experience.

Set up your first voice AI agent with Bolti

Calculating and optimizing your SIP trunking costs for voice AI is the best way to scale your outbound sales, support, or scheduling operations without breaking the bank. Whether you want to use Bolti's pre-configured telecom routes or connect your own custom SIP trunk via BYOC, you can get started in minutes.

Spin up your first multilingual voice agent today and receive 50 free minutes of call time—start your free trial on Bolti and experience sub-second latency telephony built for production.

Frequently Asked Questions

What is BYOC in voice AI?

BYOC stands for Bring Your Own Carrier. It allows you to connect your existing telephony provider (like Twilio, Plivo, Tata Communications, or Exotel) to your voice AI platform via SIP trunking. This lets you retain your business phone numbers and benefit from wholesale telecom rates.

How much does SIP trunking cost per minute in India?

SIP trunking rates in India generally range from ₹0.30 to ₹1.50 per minute for domestic calls, depending on whether the call is inbound or outbound, and the volume commitments you have negotiated with your carrier.

Does Bolti support custom SIP trunks?

Yes. Bolti allows you to bring your own SIP trunk (BYOC) from carriers like Twilio, Plivo, or Exotel, or you can use Bolti's pre-configured numbers out of the box.

How do LLM and TTS choices affect the cost per minute?

Text-to-Speech (TTS) is billed by character count, and LLMs are billed by token count. Choosing ultra-realistic models can increase your costs, while optimized open-source models (like those run on Baseten) can reduce your AI pipeline costs significantly.