Romain
Untereiner

Hands-on CTO

I build products from zero, then scale the platform and the team behind them. Open to founding and product engineering roles. Based in Barcelona.

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Things I've built

Cantoo: a cloud telecom operator, built from zero

Voice, SMS and phone numbers for service providers, behind one API. I designed and built the platform end to end: SIP edge, media servers, a real-time routing engine and a streaming billing pipeline on Kubernetes.

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Cantoo architecture: service providers send traffic and API calls to the platform; a SIP edge (Kamailio) and an SMS gateway feed a real-time routing engine that picks carriers by cost, quality and latency; FreeSWITCH media servers handle calls; usage events flow through Pulsar into ClickHouse for real-time billing; everything runs on Kubernetes on GCP and AWS.Kubernetes on GCP and AWSService providerswhite-label customersSIP edgeKamailioSMS gatewaymessagingRouting enginecost · quality · latencyMedia serversFreeSWITCHAPI & portalprovisioningPulsarusage eventsClickHousereal-time billingCarriersUK · FR · DE operator
Simplified architecture of the Cantoo platform

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Recent thoughts

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Building a Profitable Startup Without VC Money

How Cantoo went from idea to €400k annual revenue and acquisition in under two years, without raising a round. The decisions that mattered and the ones that turned out to be noise.

Why Telecom Engineers Make Great CTOs

Distributed systems, real-time constraints, regulatory compliance, and protocols that predate the web. The telecom background that shaped how I think about building products at scale.

Architecture Decisions You Can't Undo

Some technical choices compound for years. From Cantoo's distributed voice infrastructure to OneRagtime's data pipeline: lessons on the decisions that define a product's trajectory.

Building something?

I'm open to founding and product engineering roles at early-stage teams, and to a few advisory engagements on security and architecture.

Get in touch