Lead VOIP Engineer (FreeSWITCH & Kamailio)

Department: Engineering

Location: Berlin

Employment Type: FullTime

Synthflow AI is an enterprise AI agent platform that unifies customer operations across voice, chat, and messaging. Our agents handle routine interactions at scale so teams can focus on high-value work.

• Over 20M hours of operations automated

• 60% more calls answered vs. non-AI operators

• 150M interactions handled, 99.99% uptime

Backed by Accel, Atlantic Labs, and Singular. Trusted by 1,000+ customers. Recognized as one of the most promising companies in Germany.

Lead VOIP Engineer (FreeSWITCH & Kamailio)

Location: Berlin/Remote
Job Type: Full-Time
Experience Level: Senior

About the Role

We are seeking an experienced VOIP Engineer with a strong background in FreeSWITCH and Kamailio to join our team. The ideal candidate will have extensive experience in SIP-based communications, RTP streaming, and conferencing solutions, along with a deep understanding of high-load production environments. You will be responsible for designing, implementing, and optimizing scalable VOIP solutions while ensuring high availability and performance.

Responsibilities

• Design, deploy, and maintain FreeSWITCH and Kamailio-based VoIP solutions.

• Configure and troubleshoot SIP protocols, RTP streams, and media gateways.

• Monitor and optimize high-load production FreeSWITCH and VOIP systems.

• Implement and manage SIP monitoring tools like Homer or other real-time debugging solutions.

• Develop and fine-tune call routing, failover mechanisms, and load balancing strategies.

• Ensure security, scalability, and redundancy in the VoIP infrastructure.

• Troubleshoot and resolve VoIP-related issues in production environments.

• Collaborate with development, DevOps, and support teams to improve system performance.

• Work with SIP Trunks, SBCs (Session Border Controllers), and Media Servers.

• Implement WebRTC-based voice and video solutions.

• Document system configurations, troubleshooting guides, and best practices.
  

Requirements

• 5+ years of experience in VOIP engineering, particularly with FreeSWITCH and Kamailio.

• 3 years of experience with k8s on production systems is a must have.

• Strong expertise in SIP protocol, RTP streaming, and VoIP call flows.

• Experience working in high-load production FreeSWITCH environments.

• Hands-on experience with Homer SIP capture or similar SIP monitoring tools.

• Deep understanding of NAT traversal, STUN/TURN, WebRTC, and ICE frameworks.

• Strong knowledge of load balancing, failover strategies, and traffic optimization.

• Proficiency in Linux administration, networking, and troubleshooting.

• Experience with database integration (Redis, PostgreSQL, or NoSQL solutions).

• Familiarity with WebRTC, Asterisk, OpenSIPS, or RTP Proxy is a plus.

• Ability to write Bash/Python (or Golang) scripts for automation and monitoring.

• Strong problem-solving skills and ability to work in highly available and scalable environments.

Founded in Berlin in 2023 by serial entrepreneurs Albert Astabatsyan, Hakob Astabatsyan, and Sassun Mirzakhan-Saky, Synthflow AI democratizes access to advanced voice AI with a no-code platform that lets enterprises easily create, deploy and scale natural-sounding, cost-effective voice agents tailored to their business needs.