Senior / Experienced Software Developer (VoIP / SIP) Location: Guildford (Hybrid) – must live within a 2-hour commute Salary: £55,000 – £65,000 (DOE) The Opportunity An established technology business is looking for a Senior / Experienced Developer to join a small, specialist software team. You’ll help evolve an enterprise-level SIP platform and build secure, scalable services and integrations. The Role Design, develop and enhance a SIP/VoIP platform and associated services Build REST APIs and value-add services Integrate with external systems including AI-driven voice, transcription and analytics services Troubleshoot SIP/RTP issues and improve platform reliability Contribute to secure development practices and compliance (ISO27001, PCI-DSS) Key Skills & Experience Strong SIP / VoIP protocol knowledge (SIP, SDP, RTP) 5 years’ experience with Python or another OO language REST APIs, Flask/Django and secure systems development Linux (Ubuntu), Docker and Git-based workflows Wireshark for SIP/RTP troubleshooting Excellent communication skills Desirable FreeSWITCH, Kamailio or WebRTC C/C++, OAuth2/Auth0 CI/CD, Kubernetes, MongoDB or MySQL Benefits 24 days’ holiday bank holidays Hybrid Working (1 day per month in office) Pension, Life Insurance & Private Medical Birthday & volunteering day off Discounts & Cycle to Work scheme The client is looking to fill this opportunity immediately, so please apply ASAP or feel free to drop me an email with any questions to owen @ serlimited. com. SER-IN