Short answer
Short answer: IT companies in India use VoIP in two ways: as internal communications (office PBX, remote teams, client calls, Teams or Slack integration) and as a product capability (click-to-call, a dialer or voice agent embedded in their own software). The architecture and the build-vs-buy answer are different for each, and mixing them up is the most common and costly mistake.
By Pankaj Joshi, Telecom Solutions Architect. Last reviewed: October 2026.
Who this guide is for
- IT services and software firms modernising their office and remote-work telephony
- SaaS founders who want to add calling, a dialer or a voice agent to their product
- CTOs comparing a CPaaS API with a custom FreeSWITCH or Kamailio stack
Two very different problems
| Problem | Goal | Typical answer |
|---|---|---|
| Internal telephony | Reliable calls for staff across offices and homes | Hosted PBX or Teams calling with SIP trunks |
| Product telephony | Voice as a feature customers pay for | CPaaS API, or a custom multi-tenant voice platform |
Decide which one you are solving before comparing vendors.
Internal telephony: what matters
- Multi-office and remote support: extensions that follow people, softphone and mobile apps.
- SIP trunk quality and redundancy: at least two carriers, failover, number portability.
- Integration: Microsoft Teams direct routing, Slack, Google Workspace, helpdesk and CRM click-to-call.
- Security: TLS and SRTP, fraud and toll-abuse protection, restricted international dialing.
- Reporting: call logs and recordings for client SLAs and support teams.
Product telephony: building voice into your SaaS
Typical features are click-to-call from your web app, a sales or support dialer, call recording and transcription, AI summaries, and an AI voice agent. The questions that decide success are architectural:
- Tenancy: how do you separate customers’ numbers, calls, recordings and billing?
- Scale: how many concurrent calls per node, and what happens when a node fails?
- Quality: WebRTC to SIP bridging, TURN servers, codecs, jitter and packet-loss handling.
- Metering: minutes, speech usage and storage turned into invoices.
- Compliance: DND and DLT handling for outbound customers in India.
Reference architecture for a voice SaaS
| Layer | What it does | Typical technology |
|---|---|---|
| Carrier / SIP | Numbers, termination, failover | Multi-carrier SIP trunks |
| Edge and signalling | Authentication, load balancing, tenant routing, rate limiting | Kamailio or OpenSIPS |
| Media | Calls, IVR, conference, recording, WebRTC bridging | FreeSWITCH, plus RTP engine where needed |
| Voice AI | Transcription, summaries, voice agent | Streaming STT/TTS, LLM with tool calls |
| Platform API | Tenants, numbers, calls, webhooks, usage | NestJS or FastAPI, PostgreSQL, Redis |
| Frontend | Softphone, admin console, analytics | React, WebRTC |
| Billing and observability | Metering, invoices, call quality metrics, alerts | Usage pipeline, Prometheus/Grafana |
Build vs buy vs embed
| Option | Best when | Watch out for |
|---|---|---|
| CPaaS API (programmable voice) | You need to ship in weeks and volumes are modest | Per-minute margin shrinks as you scale; less control over routing and data |
| Hosted PBX / Teams calling | Internal telephony only | Not designed to be resold or embedded |
| Custom open-source platform | Voice is a core revenue line or you need custom routing, white-labelling and data control | Requires telecom engineers, monitoring and carrier management |
| Hybrid | Start on CPaaS, move high-volume flows to your own stack later | Design the abstraction layer now so you can switch without rewriting the product |
For startups, the hybrid path is usually the most capital-efficient: prove demand on an API, then move volume to your own media layer once unit economics justify it.
India-specific points
- Telecom licensing and resale: reselling voice services may need telecom licences or registered partners. Confirm with a telecom lawyer before you sell minutes.
- Work-from-home telephony: government relaxations for remote work and OSP rules have changed in recent years. Check current guidance for BPO-style operations.
- TRAI and DLT for outbound campaigns you enable for customers.
- DPDP Act: recordings and transcripts are personal data. Plan retention and deletion per tenant.
Cost drivers and timeline
Concurrent calls, monthly minutes, speech and AI usage, recording storage, tenancy requirements and uptime targets. Internal PBX migrations are usually quick; a multi-tenant voice SaaS is a product build and needs a phased roadmap. Proof on this site: Multi-tenant IP PBX / UCaaS platform covers a related architecture (honest gaps, no invented channel counts).
FAQ
Should an IT company use Teams calling or a separate PBX? If your staff already live in Microsoft Teams, Teams with SIP trunk routing is often simplest. Choose a PBX when you need contact-centre features, custom routing or non-Teams endpoints.
How do I add calling to my SaaS product? Start with a CPaaS API for click-to-call and recording, hide it behind your own abstraction layer, and move heavy flows to your own platform when volume justifies it.
Kamailio, FreeSWITCH or Asterisk? They solve different layers. Kamailio handles signalling and scale, FreeSWITCH and Asterisk handle media and call logic. Many production systems use Kamailio in front of FreeSWITCH.
How many concurrent calls can one FreeSWITCH server handle? It depends on codecs, transcoding, recording, IVR and AI streaming. Test with your real call flows rather than relying on a generic number.
Do I need a telecom licence to resell voice in India? Possibly. It depends on what you resell and how. Get legal advice early, because the answer affects your architecture and vendor choices.
Related industries
Browse all vertical guides on the India industry VoIP hub. Sibling domains:
Engineering lanes
- VoIP & SIP engineering
- AI voice agent development
- Contact center & dialer builds
- WebRTC & softphones
- SaaS & multi-tenant backends
- Architecture consulting
Pre-development architecture review
Planning voice for IT Companies? Book a scoped architecture review before you hire a development team: diagram, compliance checklist and build-vs-buy recommendation.