Telephony Engineer

Telephony Engineer About HappyRobot HappyRobot is the AI-native operating system for the real economy—a system that closes the circuit between intelligence and action. By combining real-time truth, specialized AI workers, and an orchestrating intelligence, we help enterprises run complex, mission-critical operations with true autonomy. Our AI OS compounds knowledge, optimizes at every level, and evolves over time. We're starting with supply chain and industrial-scale operations, where resilience, speed, and continuous improvement matter most—freeing humans to focus on strategy, creativity, and other high-value tasks. You can learn more about our vision in our Manifesto. HappyRobot has raised $62M to date, including our last $44M Series B in September 2025. Our investors include Y Combinator (YC), Andreessen Horowitz (a16z), and Base10—partners who believe in our mission to redefine how enterprises operate. We're channeling this investment into building a world-class team: people with relentless drive, sharp problem-solving skills, and the passion to push limits in a fast-paced, high-intensity environment. If this resonates, you belong at HappyRobot. About the Role We're looking for a Telephony Engineer based in Madrid to own and scale the real-time voice infrastructure that powers HappyRobot's AI workers across Europe. You'll be the go-to person for everything telephony on this side of the Atlantic—from SIP trunking and SBC configuration to CCaaS integrations and network troubleshooting. Our European client base is growing fast across large-scale logistics, telcos, and enterprise operations, and we need someone who can deploy, debug, and evolve our voice infrastructure with the same speed and ownership mindset that defines the rest of the team. You'll work closely with our US-based telephony lead and the Forward Deployed Engineering team embedded with customers. This is a high-agency role. You won't be handed runbooks—you'll write them. If something breaks, you fix it. If a customer needs a trunk stood up by tomorrow, you make it happen. If a process doesn't exist yet, you build it. Responsibilities - Own and operate European SBC infrastructure (OpenSIPS/Kamailio). Configure, monitor, and troubleshoot SIP trunks for enterprise clients. Ensure high-availability voice delivery with sub-second failover. - Integrate AI voice agents with CCaaS/UCaaS platforms such as Genesys Cloud, Five9, NICE CXone, RingCentral, Zoom, 8x8, and others. Handle OAuth flows, SIP header parsing, queue routing, and agent-availability checks. - Diagnose call quality issues—latency, jitter, one-sided audio, codec negotiation failures—using Wireshark, tshark, mtr, and ffmpeg. Capture and analyze SIP call flows end-to-end. - Optimize call flows, IVRs, routing logic, and contact center performance across client deployments. - Support trunk provisioning and incident resolution with carriers and telephony vendors as needed. - Maintain and improve telephony infrastructure in Kubernetes. Write automation scripts and tooling in Golang, JavaScript, or Python. Contribute to CI/CD pipelines and monitoring. - Join technical calls with enterprise clients and their telephony partners. Translate complex SIP and networking issues into clear language for non-technical stakeholders. - Create and maintain documentation on infrastructure, integrations, and procedures. - Help evaluate and deploy next-generation real-time communication tools (LiveKit, WebRTC) as the voice stack evolves. Requirements - Deep SIP/VoIP expertise. You can read a SIP call flow in your sleep. You understand INVITEs, REGISTERs, codecs (PCMU, PCMA, G722), SRTP, DTMF (RFC 2833), and one-sided audio debugging. - OpenSIPS or Kamailio experience. Hands-on experience configuring, scaling, and troubleshooting SIP proxy servers is essential for this role. - Strong networking fundamentals. TCP/UDP, DNS, TLS, NAT traversal, firewall rules, port management. Proficient with Wireshark/tshark, ... (truncated, view full listing at source)