PBX / VoIP Systems Architect (Fractional / Part-Time)

About Us Yottavox is building a new cloud-hosted PBX platform engineered for clarity, security, and modern scalability. We are developing the platform from the ground up and are now seeking an experienced VoIP & PBX Systems Architect to guide the technical direction, validate decisions, and ensure our solution meets telecom-grade standards. This role is for someone who has architected PBX or cloud telephony platforms end-to-end and understands how PBX application logic interacts with SIP signalling and media engines. The Role You will be responsible for architecting the PBX application layer and ensuring it integrates cleanly with the SIP core and media engine. Your focus will be: • designing multi-tenant PBX behaviour (IVR, queues, routing, call flows)• defining backend logic and data models • shaping signalling and media handling at a high level • guiding our full stack VoIP developer • ensuring the platform follows modern PBX patterns and telecom best practice This is an architectural and advisory position, not a full-time coding role and will be working closely with the founders, design team, software and full-stack VoIP developers. Key Responsibilities 1. Architecture & System Design Design the full PBX application architecture for a multi-tenant cloud platform. Model tenants, extensions, IVRs, queues, call routing, recording and CDR behaviour. Define how backend logic generates call instructions and interacts with FreeSWITCH. Shape SIP signalling flows and RTP/media handling at the architectural level. Produce clear HLD and LLD diagrams, call flow documentation and domain models. 2. Technical Direction & Decision-Making Recommend and justify technology choices (FreeSWITCH, Asterisk, Kamailio/OpenSIPS, backend stack). Evaluate design trade-offs and identify architecture risks early. Ensure the backend, SIP layer and UI all align with PBX feature requirements. 3. Oversight & Engineering Guidance Guide and review the work of the developer team Provide structure for implementing IVRs, queues, routing logic, CDRs, recordings and event models. Ensure the system behaves predictably under load and follows telecom best practices. 4. Security, Reliability & Performance Define safe-by-default patterns for SIP/TLS/SRTP, fraud prevention, rate limiting, and access control. Ensure the architecture supports low latency, resilience, and future scalability. Advise on disaster recovery, redundancy, monitoring, and analytics requirements. 5. Documentation & Clarity Produce clear architectural documentation that supports efficient development. Document key decisions, flows, constraints, and rationale. Help create a system that is maintainable and easy for new engineers to understand. 6. Collaboration & Delivery Support Work closely with UI/UX during design and with engineering during build. Participate in milestone reviews and provide structured feedback. Assist in planning a vertical slice for early validation. Required Experience Extensive experience architecting VoIP/PBX/SIP platforms. Strong understanding of PBX features such as IVR flows, queues, routing rules, multi-tenant logic, recordings and CDR design. Deep understanding of SIP, RTP, NAT traversal, codecs, and media behaviour. Strong background with Asterisk, FreeSWITCH, Kamailio/OpenSIPS, or similar. Experience designing secure telecom systems using SRTP/TLS and fraud controls. Familiarity with cloud infrastructure, containerisation, and scalable system design. Ability to communicate complex PBX and VoIP concepts clearly and simply. Desirable Experience with multi-tenant SaaS architecture. Knowledge of global trunking integrations and number routing. Understanding of call recording pipelines, CDR accuracy, and observability. Experience supporting early-stage or startup-style product builds. Why Join Us Shape a brand-new PBX platform without legacy constraints. Flexible fractional engagement - ideal alongside existing consulting roles. Work directly with a founder who values clarity, quality, and efficient execution. Influence architecture from day one and help build a future-ready telecom platform. Job Type: Fractional - Part Time / Contract Benefits: Flexitime Work from home Work Location: Remote