Key takeaways
- SIP trunk providers vary significantly on coverage, pricing, API quality, and India-specific features
- For India-focused businesses, local billing in INR, 140-series number support, and TRAI compliance matter as much as per-minute rates
- AI voice agent platforms (Retell, Vapi, ElevenLabs) connect to SIP trunks — not to carriers directly
- Vobiz is built for India: ₹0.45/min, 10-digit numbers, 140-series lines, INR invoicing, self-serve API
- Global providers (Twilio, Telnyx, Vonage) work but cost 2–4× more for India termination
What SIP Trunking Actually Does
A SIP trunk is a logical channel between your system (PBX, Asterisk, FreeSWITCH, Kamailio, or cloud voice platform) and the carrier’s network. SIP handles call setup and teardown; RTP carries the actual audio.5 Criteria to Evaluate SIP Trunk Providers
1. Geographic Coverage
Does the provider have phone number inventory (DIDs) in every country you need? Can they terminate (send) calls to those destinations? For India, also check: does the provider have 10-digit mobile DIDs, 140-series business lines, and toll-free 1800 numbers?2. Pricing and Billing Currency
Per-minute rates differ 3–5× between providers on the same route. For India-based businesses, billing in INR matters: USD billing means forex exposure, and many global providers charge India termination at $0.015–0.025/min (~₹1.25–2.00/min) versus ₹0.45–0.80/min on a local carrier.3. Concurrency Limits and Scaling
How many simultaneous calls can you run? Some providers have hard caps that require pre-approval. Others allow you to burst on demand. For AI voice agents running outbound campaigns, you may need 200–500 concurrent channels at peak.4. API and Programmability
Can you provision phone numbers, trunks, credentials, and origination URIs via API? For teams building voice products, a programmatic API is not optional — you need to onboard customers, rotate DIDs, and configure trunks without touching a UI. Rate limits on the API matter too.5. Latency and Infrastructure Location
For India-originated and India-terminated calls, the provider’s points of presence (PoPs) should be in Mumbai, Delhi, or Chennai. A PoP in Singapore adds 50–80ms of latency to every call. For AI agents where the full ASR→LLM→TTS loop already takes 500–800ms, adding carrier latency pushes the total beyond the 1,000ms threshold where callers notice the delay.SIP Trunk Provider Comparison
Rates are estimates for India termination, excluding taxes. Verify current rates with each provider.
SIP Trunking for AI Voice Agents
AI voice agent platforms do not directly connect to phone carriers — they connect to SIP trunk providers. The architecture is:Outbound vs Inbound SIP Trunking
Outbound trunk (also called termination): Your system sends calls OUT through the provider. Authentication is by SIP digest credentials (username + password) or IP allowlist. The provider bills per minute for each connected call. Inbound trunk (also called origination): Calls come IN from the PSTN to your system. You configure a DID number to route to your SIP endpoint URI. The provider bills per minute for inbound minutes. For a full AI receptionist setup, you need both: an outbound trunk so your agent can dial out, and an inbound trunk so callers can reach your agent on a real number.Vobiz SIP Trunk Quickstart
Vobiz is designed for Indian market voice infrastructure — built-in TRAI compliance, 140-series business numbers, INR billing, and a full API for programmatic provisioning. Get started in 5 minutes:- Create an account at console.vobiz.ai
- Buy a phone number (10-digit mobile, 140-series, or toll-free)
- Navigate to SIP Trunk → Outbound Trunks → Create Trunk
- Copy your SIP domain (
yoursubdomain.sip.vobiz.ai), username, and password - Enter these into your PBX or AI agent platform
SIP Trunk Pricing: What You Actually Pay
SIP trunk pricing has four components that are rarely shown together:
A business running 10,000 minutes/month of outbound calls on 2 numbers pays roughly ₹4,500–8,000/month in total on Vobiz. The equivalent on Twilio at ~₹1.83/min would be ~₹18,300/month — over 2× more.
India-Specific Requirements
140-series numbers: The Telecom Regulatory Authority of India (TRAI) requires business-to-consumer voice calls to originate from 140-series numbers, not standard mobile numbers. Vobiz is one of the few providers with self-serve 140-series number provisioning. DLT registration: If your calls involve promotional or transactional communication, the principal entity must be registered on the Distributed Ledger Technology (DLT) platform. Vobiz supports this compliance workflow. KYC: Indian telecom regulations require identity verification before activating numbers. Vobiz’s self-serve KYC process completes in minutes. GST invoicing: Vobiz issues GST-compliant invoices in INR, simplifying accounting for Indian businesses.Next Steps
- Read the SIP trunking concept guide for a deeper technical reference
- Create a Vobiz account and provision your first trunk
- Compare Vobiz vs Twilio for a detailed pricing breakdown
- Compare Vobiz vs Telnyx if you’re evaluating US/EU providers