Senior Software Developer (Voice / SIP Platforms)

£55,000 £65,000 DOE | Hybrid Working (1x day a month office)

Are you a seasoned developer with a passion for building robust, real-time communications platforms? Looking for a role where you can work on complex, enterprise-grade systems while still being close to the technical detail?

This is an opportunity to join a well-established technology business with a strong reputation in communications and cloud-based solutions. Youll be part of a small, highly skilled development team working on the evolution of a large-scale SIP platform and its associated APIs, with plenty of scope to influence design, tooling, and future direction.

The Role

Working closely with the Development Manager, youll play a key role in enhancing and extending an existing SIP and VoIP platform used in production environments. This is a hands-on role suited to an experienced developer who enjoys solving complex protocol-level problems, building secure services, and integrating with third-party systems.

Youll contribute across the full software lifecycle from design and development through to troubleshooting live issues while helping to improve development standards, security practices, and platform resilience.

Key Responsibilities

Design, develop, and enhance a production SIP/VoIP platform and supporting services

Build additional value-added services and integrations around the core platform

Develop integrations with external systems, including AI-driven services such as speech recognition, transcription, and analytics

Ensure secure design and implementation across software and infrastructure

Diagnose and resolve complex SIP, RTP, and platform-level issues

Contribute to secure development processes and compliance with recognised security standards (e.g. ISO27001, PCI-DSS)

Collaborate closely with other engineers and stakeholders, sharing knowledge and best practice

Essential Skills & Experience

Strong, hands-on experience with SIP/VoIP technologies and protocols (e.g. SIP, SDP, RTP, RFC2833/4733)

5+ years experience developing in Python or another object-oriented language

Solid understanding of object-oriented design principles

Experience building and consuming HTTP/REST APIs

Familiarity with Python frameworks and tooling such as Flask or Django, Pytest, SQLAlchemy, Marshmallow

Strong background in secure systems design (software and network level)

Proven experience using Wireshark for SIP/RTP analysis and fault-finding

Version control experience with Git-based platforms

Containerisation using Docker

Strong Linux experience (Ubuntu-based systems)

Excellent communication skills, comfortable working with both technical and non-technical stakeholders

Desirable / Nice to Have

Experience with FreeSWITCH (configuration and/or source code exposure)

Working knowledge of C or C++

Experience with Kamailio

Authentication and authorisation frameworks (OAuth2, Auth0)

Databases such as MongoDB and MySQL

CI/CD pipelines (e.g. GitHub Actions)

Kubernetes, ArgoCD, or similar deployment tooling

WebRTC experience

Whats on Offer

Salary up to £65,000 depending on experience

Hybrid working model

24 days annual leave plus bank holidays

Pension and life assurance

Private medical insurance

Birthday day off and paid volunteering day

Cycle to Work scheme

Retail and lifestyle discount programmes

Interested?

If youre an experienced developer looking to work on technically challenging, real-time systems in a supportive and forward-thinking environment, wed love to hear from you. Apply now to learn more.

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