Introducing the Callr Tech Blog: a closer look at our telco infrastructure

Running a telephony network is an unforgiving engineering problem. We’ve spent years building and operating one, and we’ve decided it’s time to share more of what we’ve learned. That’s why we launched the Callr Tech Blog — a place to go deep on the systems, the trade-offs, and the tools that keep voice and messaging flowing.

Why open up the engineering side

Our main blog has always covered telco topics for a broad audience: how communications power the sharing economy, how AI agents change customer interactions, the occasional hands-on tutorial built around our REST API. We’ve worked hard to keep that writing accessible to non-technical readers.

But telephony is a genuinely hard technical challenge, and we’ve wanted to dig into the details for a long time. The Tech Blog is where we do that — written by the engineers who build and run the platform, for the engineers who care about the same problems.

Why latency is the whole game

Voice is far less forgiving than the web. A slow web request is annoying; a slow phone call is broken. As our CTO Florent puts it:

“In the telco world, latency is everything. If your web app is overloaded and a request takes five seconds to reply, that’s painful — but it still works. On a phone call, latency eventually breaks the line. A 250 ms delay is enough to make audio choppy.”

That constraint shapes nearly every decision we make about routing, signalling, and infrastructure. It’s also why the lessons translate well beyond telephony: anyone wrestling with scalability and latency at scale will recognise the same battles.

Open-sourcing our tools

The Tech Blog isn’t just writing — we’re releasing some of the tooling we use in production. We’re starting with a Kamailio exporter for Prometheus, so other teams running SIP infrastructure can get proper observability into their stack.

The telco community has historically kept its solutions to itself. The wider web runs on shared code, shared experience, and shared fixes — and we think operating a telephony platform should be no different. Contributing back is overdue, and this is our first step.

Dive in

The Callr Tech Blog covers our engineering work, the technologies behind the platform, and how we build our products. If you care about voice, SIP, observability, or simply pushing systems to their limits, come take a look.