I run a dev shop called Crudloop. With the UK PSTN copper network shutting down in 2027, I noticed many businesses panic-buying SaaS subscriptions (RingCentral/Webex/8x8) at ~£25/user/mo, despite wholesale SIP trunking costing fractions of a penny.
We spent the last 6 months engineering a production-ready VoIP stack to solve this.
The Business Model: This is not a SaaS and it is not Open Source. Instead of renting seats, I license the source code and deploy the entire stack to your private VPS (AWS/Hetzner/DigitalOcean). You pay a one-time fee for the code/setup, and then you pay wholesale rates directly to the carrier (Telnyx).
The Infrastructure: - Backend: Django (DRF) + Celery + Redis. Handles dynamic routing via Telnyx Webhooks (TeXML). Scalable via Docker Swarm/K8s. - Web: React + TanStack Query + @telnyx/webrtc SDK. - Mobile: Native iOS (Swift) integration for reliable background calls.
The Economics: For a company with 30 employees, switching from a £25/user SaaS to this private stack saves ~£8,000/year and guarantees data sovereignty. You own the metal, you own the logs, and you control the routing logic.
I'm looking for agencies or SMEs who want to own their infrastructure.
Happy to answer questions about self-hosting economics, scaling Django for real-time SIP events, or maintaining a private VoIP cloud.